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        <!-- Passage 1: Easy — Technology                                 -->
        <!-- CEFR B1 | ~380 words | Academic Reading Section 1            -->
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        <record id="passage_technology" model="encoach.passage">
            <field name="exam_type">academic</field>
            <field name="section_num">1</field>
            <field name="topic_category">Technology</field>
            <field name="difficulty">easy</field>
            <field name="status">active</field>
            <field name="approved" eval="True"/>
            <field name="ielts_certified" eval="True"/>
            <field name="cefr_level">b1</field>
            <field name="body_text">The Rise of Artificial Intelligence in Everyday Life

Artificial intelligence, once confined to science fiction novels and academic research laboratories, has become an integral part of daily life for millions of people worldwide. From the moment we wake up to an alarm set by a smart assistant to the personalised news feed we scroll through over breakfast, AI systems are quietly working behind the scenes to make our routines more convenient and efficient.

One of the most visible applications of AI is in virtual assistants such as Siri, Alexa, and Google Assistant. These systems use natural language processing to understand spoken commands and provide relevant responses. Whether it is setting a reminder, playing a song, or answering a factual question, these assistants have become household staples in many countries. Studies show that over 40 percent of adults now use voice-activated assistants at least once a day.

Recommendation algorithms represent another pervasive form of AI. Streaming platforms like Netflix and Spotify analyse viewing and listening habits to suggest content that users are likely to enjoy. Online retailers employ similar technology to recommend products based on browsing history and past purchases. While these systems can feel remarkably intuitive, they work by identifying patterns in enormous datasets and applying statistical models to predict preferences.

In healthcare, AI is making significant strides. Machine learning algorithms can now analyse medical images with accuracy that rivals trained radiologists in certain tasks. Diagnostic tools powered by AI help doctors identify conditions ranging from skin cancer to diabetic retinopathy at earlier stages. However, these tools are designed to assist rather than replace medical professionals, and their outputs still require clinical interpretation.

Transportation is another sector being transformed by artificial intelligence. Navigation applications use real-time traffic data and predictive models to suggest optimal routes. Ride-sharing services employ AI to match passengers with drivers and calculate dynamic pricing. Meanwhile, autonomous vehicle technology continues to advance, with several companies conducting trials of self-driving cars on public roads.

Despite these benefits, the growing presence of AI raises important questions. Concerns about data privacy, algorithmic bias, and the potential displacement of jobs have prompted calls for stronger regulation and ethical guidelines. As AI becomes more capable, society must grapple with how to harness its potential while mitigating its risks.</field>
        </record>

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        <!-- Passage 2: Medium — Environment                              -->
        <!-- CEFR B2 | ~540 words | Academic Reading Section 2            -->
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        <record id="passage_environment" model="encoach.passage">
            <field name="exam_type">academic</field>
            <field name="section_num">2</field>
            <field name="topic_category">Environment</field>
            <field name="difficulty">medium</field>
            <field name="status">active</field>
            <field name="approved" eval="True"/>
            <field name="ielts_certified" eval="True"/>
            <field name="cefr_level">b2</field>
            <field name="body_text">Ocean Acidification: The Silent Threat to Marine Ecosystems

While the atmospheric consequences of rising carbon dioxide levels have received considerable public attention, a parallel crisis is unfolding beneath the surface of the world's oceans. Ocean acidification, sometimes referred to as "climate change's equally evil twin," occurs when seawater absorbs excess carbon dioxide from the atmosphere, triggering chemical reactions that lower the water's pH. Since the beginning of the Industrial Revolution, the oceans have absorbed approximately 30 percent of all human-produced CO2 emissions, causing surface water pH to drop by 0.1 units. Although this figure may appear modest, it represents a 26 percent increase in hydrogen ion concentration, fundamentally altering ocean chemistry on a global scale.

The process is deceptively straightforward. When CO2 dissolves in seawater, it reacts with water molecules to form carbonic acid, which then dissociates into hydrogen ions and bicarbonate. The surplus hydrogen ions bond with carbonate ions, reducing their availability in the water. This is particularly consequential because carbonate ions are essential building blocks for the calcium carbonate structures produced by a wide range of marine organisms, including corals, molluscs, sea urchins, and certain species of plankton.

Coral reefs, which support roughly 25 percent of all marine species despite covering less than one percent of the ocean floor, are among the most vulnerable ecosystems. As carbonate ion concentrations decline, corals struggle to build and maintain their skeletal frameworks. Research conducted at multiple reef sites has demonstrated that calcification rates have already decreased by 14 percent compared to pre-industrial levels. In severely acidified conditions, existing coral structures may begin to dissolve, threatening the intricate habitats upon which countless species depend.

The implications extend beyond reef-building organisms. Pteropods, tiny sea snails that form a critical component of Arctic and Antarctic food webs, produce delicate shells made of aragonite, a particularly soluble form of calcium carbonate. Laboratory studies have shown that exposure to projected end-of-century pH levels causes visible shell dissolution within 48 hours. Since pteropods serve as a primary food source for species ranging from juvenile salmon to baleen whales, their decline could trigger cascading effects throughout marine food chains.

Perhaps most troubling is the speed at which these changes are occurring. Geological evidence suggests that current acidification rates are at least ten times faster than any natural event in the past 300 million years, leaving marine organisms with little evolutionary time to adapt. Some species may shift their geographic ranges toward more favourable conditions, while others may face population declines or local extinction.

Mitigating ocean acidification ultimately requires reducing CO2 emissions at their source. However, several complementary strategies are being explored, including the cultivation of seagrass beds and kelp forests, which absorb CO2 through photosynthesis and create localised refugia of higher pH. Researchers are also investigating selective breeding programmes aimed at identifying and propagating acid-resistant genetic variants of key species. While these approaches show promise, scientists emphasise that they cannot substitute for the fundamental changes in energy production and consumption needed to address the root cause of the problem.</field>
        </record>

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        <!-- Passage 3: Hard — Research Methodology                       -->
        <!-- CEFR C1 | ~640 words | Academic Reading Section 3            -->
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        <record id="passage_research" model="encoach.passage">
            <field name="exam_type">academic</field>
            <field name="section_num">3</field>
            <field name="topic_category">Research Methodology</field>
            <field name="difficulty">hard</field>
            <field name="status">active</field>
            <field name="approved" eval="True"/>
            <field name="ielts_certified" eval="True"/>
            <field name="cefr_level">c1</field>
            <field name="body_text">Randomised Controlled Trials: Methodological Rigour and Its Limitations

The randomised controlled trial (RCT) is widely regarded as the gold standard of evidence-based research, occupying the highest tier in most hierarchies of scientific evidence. By randomly assigning participants to experimental and control groups, RCTs minimise the influence of confounding variables and selection bias, thereby isolating the effect of the intervention under investigation. This methodological strength has made RCTs the preferred design for evaluating pharmaceutical treatments, surgical procedures, and, increasingly, educational and social policy interventions. Yet despite their epistemological advantages, RCTs are subject to a range of practical, ethical, and conceptual limitations that researchers and policymakers must carefully consider.

One fundamental challenge concerns external validity, or the extent to which findings from a controlled trial can be generalised to broader populations and real-world settings. RCTs typically employ stringent inclusion and exclusion criteria to create homogeneous study samples, which enhances internal validity but may produce results that are not representative of the heterogeneous populations encountered in clinical practice. A landmark analysis by Rothwell (2005) found that fewer than 20 percent of patients seen in routine care would have met the eligibility criteria for the trials whose results were used to guide their treatment. This discrepancy raises legitimate questions about the applicability of trial-derived evidence to individual patients with multiple comorbidities, varying genetic backgrounds, and diverse socioeconomic circumstances.

Ethical constraints further limit the scope of RCTs. The principle of equipoise demands that genuine uncertainty exist regarding the relative merits of the interventions being compared; it is ethically impermissible to randomly withhold a treatment that is believed to be superior. In emergency medicine, obtaining informed consent from patients in acute distress presents additional dilemmas that have prompted the development of exception-from-informed-consent protocols, which themselves remain controversial. Moreover, certain research questions — such as the long-term health effects of environmental pollutants or the consequences of adverse childhood experiences — cannot ethically be addressed through experimental manipulation.

The issue of blinding introduces another layer of complexity. Double-blind designs, in which neither participants nor investigators are aware of group assignments, are considered ideal for minimising performance and detection bias. However, effective blinding is often difficult or impossible to achieve, particularly in trials of surgical interventions, psychotherapy, or lifestyle modifications. When participants can discern their group allocation, placebo effects and expectation biases may contaminate outcomes, and the Hawthorne effect — whereby individuals modify their behaviour simply because they know they are being observed — can influence results in both experimental and control groups.

The increasing recognition of these limitations has spurred methodological innovation. Pragmatic trials, which relax eligibility criteria and are conducted in real-world clinical settings, represent one response to concerns about external validity. Adaptive trial designs allow modifications to sample size, dosage, or even study hypotheses based on interim analyses, potentially improving efficiency without compromising statistical rigour. Bayesian approaches offer an alternative framework for incorporating prior evidence and updating probability estimates as data accumulate.

Nevertheless, these innovations do not eliminate the fundamental tension between the controlled conditions that give RCTs their inferential power and the messy complexity of the environments in which their findings must ultimately be applied. A judicious approach to evidence-based practice requires not only high-quality RCTs but also complementary forms of evidence — including observational studies, qualitative research, and clinical expertise — synthesised through systematic reviews and interpreted with sensitivity to the specific context of application.</field>
        </record>

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