영어 모의고사 (자동 편성)

Bacteria have been cutting up invading viral DNA for billions of years, long before any scientist ①thought to borrow the trick for use in a laboratory. The CRISPR-Cas9 system, as it is now known, relies on a short guide RNA that matches a specific DNA sequence, ②lead a scissor-like enzyme called Cas9 directly to that exact location in the genome. Once Cas9 arrives at the target site, it slices both strands of the DNA helix, and the cell's own repair machinery rushes in ③to mend the cut, often introducing a small change in the process. By supplying the cell with a template during this repair step, scientists can direct that machinery ④to insert a specific new sequence rather than merely disabling the original gene. What once required years of painstaking work to alter a single gene can now, with a properly designed guide RNA, ⑤be accomplished within days, a shift in speed that has reshaped nearly every corner of biological research.

Across many countries, high schools begin classes ①early in the morning, often before eight o'clock. This schedule assumes that teenagers can simply go to bed earlier to compensate, but biology tells a different story. During adolescence, the body's internal clock shifts ②earlier, delaying the release of melatonin until well after ten at night. As a result, most teenagers are not physiologically ready to fall asleep until much later than younger children or adults. When early start times force them to wake before their bodies have completed a full sleep cycle, the mismatch ③accumulates into a chronic sleep debt that affects concentration and mood throughout the school day. Researchers who study this mismatch argue that the underlying problem is not laziness or poor discipline among students, but a scheduling system built around adult rhythms rather than ④adolescent ones. Some school districts that delayed their start times by thirty minutes reported ⑤measurable improvements in attendance.

Across the world, teenagers are chronically short on sleep, often getting two or three hours less than the eight to ten hours experts recommend for their age. Part of the problem lies in biology: as puberty begins, the body's internal clock naturally ①shifts later, making it difficult for teenagers to fall asleep before eleven at night. Yet school start times rarely adjust to this shift, forcing students to wake before their bodies are ready. The consequences extend well beyond simple tiredness. Chronic sleep loss during adolescence has been linked to ②impaired concentration, weakened memory, and a higher risk of anxiety and depression. It can also disrupt the hormones that regulate appetite, contributing to ③unhealthy weight gain over time. Some school districts have experimented with delaying start times by even thirty minutes, and early results suggest that students who gain that extra rest show ④worsened grades, better mood, and fewer tardy arrivals. Despite this evidence, changing entrenched school schedules remains a slow and ⑤contentious process.

A flexitarian is someone who mainly eats plant-based meals but occasionally includes meat or fish, unlike a strict vegetarian who avoids animal products entirely. This flexible diet has recently gained attention as a practical way to fight climate change, since raising livestock produces a significant portion of global greenhouse gas emissions. Cattle, in particular, release large amounts of methane, a gas far more powerful than carbon dioxide at trapping heat in the atmosphere. By replacing just a few meat-based meals each week with vegetables, grains, or legumes, individuals can noticeably shrink their carbon footprint without giving up meat completely. Nutritionists also emphasize that flexitarian eating is easier to maintain than full vegetarianism, because it allows flexibility rather than demanding absolute discipline. Therefore, many environmental groups now promote flexitarianism as a realistic first step, believing that _______________.

Researchers who study teenagers have found a strong link between how well students sleep and how well they perform in school. Students who sleep fewer than seven hours a night tend to score lower on tests of memory and attention than those who sleep eight or nine hours, even when the two groups study for the same number of hours. One explanation is that sleep plays an active role in learning: during certain stages of sleep, the brain replays and strengthens information encountered during the day, _______________. When sleep is cut short, this consolidation process is interrupted before it can finish, so material that seemed well understood the night before often feels unfamiliar the next morning. For this reason, some schools have begun rethinking early start times, reasoning that an extra hour of sleep might do more for test scores than an extra hour of studying ever could.

Insomnia is rarely caused by a single factor; it usually emerges from an interaction between psychological stress and physiological arousal that keeps the body from settling into sleep. (A) At the same time, the body's stress response system can become chronically activated, releasing hormones such as cortisol that keep heart rate and body temperature elevated at night, both of which interfere with the natural drop in arousal needed to fall asleep. (B) Poor sleep habits, including irregular bedtimes and excessive screen use before bed, can further weaken the body's internal signals for sleep onset. Because these psychological and physiological factors reinforce one another, effective treatment for chronic insomnia addresses both the racing mind and the underlying pattern of physical tension, rather than relying on medication alone. (C) A common trigger is what researchers call cognitive hyperarousal, in which the mind continues to race with worries about work, relationships, or even the inability to sleep itself, creating a frustrating cycle where anxiety about insomnia becomes a cause of insomnia.

Planning a multi-city trip once meant hours spent comparing flight schedules, reading hotel reviews, and mapping out which sights were close enough to visit in a single day. (A) Many travelers appreciate having a solid starting point rather than a blank page. (B) Still, seasoned travelers warn that these itineraries can feel oddly generic, often steering users toward the same popular landmarks that every other AI-generated plan recommends. (C) AI travel planners now compress much of that work into a short conversation, generating a full day-by-day itinerary within minutes based on enormous amounts of data.

During sleep, the brain does not simply rest; it actively reorganizes the day's experiences into lasting memories through a process called consolidation. (A) Sleep researchers have demonstrated this effect experimentally: participants who slept after learning a list of word pairs recalled more items the next day than participants who remained awake instead. Crucially, the benefit was not limited to simple recall; sleep also seemed to help participants extract general patterns from the material, suggesting that consolidation involves more than passive storage. (B) Newly formed memories are initially fragile and stored primarily in a brain region called the hippocampus, which has limited long-term capacity. (C) While a person sleeps, particularly during the deep stages of non-REM sleep, neural activity replays these fresh memory traces in rapid, compressed sequences, gradually transferring the information to the cortex for more durable, long-term storage. This replay strengthens the connections between neurons that encoded the original experience, making the memory more resistant to interference from unrelated events the following day.

This connection is not merely correlational; sleep appears to directly supply the raw materials the immune system needs. When the body fights off an infection, the immune system relies heavily on adequate sleep to function effectively. ( ① ) During deep sleep, the body produces and releases cytokines, proteins that help regulate immune responses and coordinate the fight against harmful invaders such as viruses and bacteria. ( ② ) People who consistently sleep fewer than six hours a night show measurably weaker antibody responses after vaccination compared with those who sleep seven or eight hours, suggesting that sleep loss can blunt the immune system's ability to build lasting protection. ( ③ ) Chronic sleep deprivation also appears to promote low-grade inflammation throughout the body, a state that, over time, has been linked to a higher risk of heart disease and other chronic conditions. ( ④ ) Rather than being a passive state in which the body simply rests, sleep functions as an active period during which the immune system repairs itself and prepares for future threats. ( ⑤ ) This is why doctors often recommend extra sleep, not just medication, when someone is fighting an illness.

In response, some platforms have begun inserting occasional wildcard suggestions that are deliberately unrelated to past viewing habits. After a viewer finishes an episode, a streaming service rarely leaves the choice of what to watch next entirely up to chance. ( ① ) Instead, a recommendation algorithm compares that viewer's habits with patterns drawn from millions of other users who watched similar content, then ranks thousands of titles in order of predicted interest. ( ② ) This approach keeps viewers engaged far longer than a simple list of new releases ever could, which is precisely why streaming companies invest so heavily in refining it. ( ③ ) The system is not without drawbacks, however. Because the algorithm favors titles similar to what a viewer already enjoys, it can quietly narrow someone's exposure to unfamiliar genres, directors, or cultures, creating a comfortable but repetitive bubble. ( ④ ) These wildcard picks are meant to counteract this narrowing effect and keep recommendations from becoming too predictable. ( ⑤ )