영어 모의고사 (자동 편성)

Across many countries, high schools ① begins classes early 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 later, ② 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 ③ to wake before their bodies have completed a full sleep cycle, the mismatch accumulates into a chronic sleep debt ④ 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 ⑤ built around adult rhythms rather than adolescent ones.

Many people struggling to fall asleep in noisy environments turn to white noise machines, devices that ① emit a steady, uniform sound covering a broad range of frequencies. The appeal lies in a phenomenon called auditory masking, in which a constant background sound makes sudden noises ② less noticeable to the sleeping brain. Without this masking effect, an abrupt change in sound is far more likely ③ to trigger a brief awakening, even if the sleeper does not consciously remember it the next morning. Studies comparing sleep in quiet rooms with sleep alongside white noise have found that participants using white noise ④ experienced fewer of these brief awakenings. However, researchers caution that the benefit depends heavily on volume and consistency, since noise that is too loud or that ⑤ varying unpredictably can itself become a source of disruption rather than a remedy.

Wearable devices ① that track sleep have become enormously popular, promising a detailed breakdown of light, deep, and REM sleep each night. These gadgets typically rely on movement sensors and heart rate monitors ② to estimate sleep stages, since directly measuring brain activity would require equipment found only in a sleep laboratory. Independent studies ③ compares wearable data with polysomnography, the gold-standard method used in clinical sleep labs, have found that consumer devices are reasonably accurate at distinguishing sleep from wakefulness but considerably less reliable at identifying specific sleep stages. Some trackers overestimate deep sleep, while others ④ underestimate the amount of time spent in REM sleep, and the margin of error can vary widely between brands. Despite these limitations, many users have come ⑤ to treat the nightly score generated by their device as an objective medical verdict, sometimes experiencing anxiety when the number falls below what they expect, a phenomenon researchers have begun calling orthosomnia.

Researchers who study teenagers have found a ① 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 ② 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, converting fragile short-term memories into more ③ durable long-term ones. 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 ④ unfamiliar the next morning. For this reason, some schools have begun ⑤ confirming early start times, reasoning that an extra hour of sleep might do more for test scores than an extra hour of studying ever could.

For centuries, dreams have fascinated scientists and philosophers alike, yet no single theory fully explains why the sleeping brain generates such vivid and often bizarre experiences. One prominent idea suggests that dreaming helps the brain process emotional experiences, _______________. Another theory proposes that dreams serve a more practical function, allowing the brain to rehearse responses to threats without any real danger, a kind of nightly simulation that may have offered early humans a survival advantage. Still other researchers argue that dreaming is simply a byproduct of the brain organizing memories, with vivid imagery arising as the mind sorts through the day's information rather than serving any independent purpose of its own.

Travelers who cross several time zones in a single flight often arrive feeling exhausted, foggy, and strangely out of sync with the local clock, a condition widely known as jet lag. The discomfort arises because the body's internal clock continues to run on the schedule of the departure city even after landing. Realigning this internal clock to a new time zone is not instantaneous; researchers estimate that the body typically needs about one day to adjust for every time zone crossed. Flying eastward tends to produce more severe symptoms than flying westward, because _______________. Exposure to natural light at the right moments after arrival can help speed up the adjustment, since light is the strongest external cue the internal clock uses to reset itself.

Melatonin is a hormone produced by a small gland deep within the brain, and its release follows a remarkably predictable daily pattern. Levels stay low throughout the bright hours of the day, begin rising in the evening as darkness falls, peak in the middle of the night, and then decline again as morning approaches. This rhythm is controlled primarily by light: specialized cells in the eye detect brightness and send signals that either permit or suppress melatonin production, which is why exposure to bright screens late at night can delay its release and make falling asleep more difficult. Unlike some hormones that directly cause the body to perform a task, _______________, preparing various systems to shift into a lower-energy state. Because of this signaling role, taking melatonin supplements at the wrong time can shift a person's internal clock in the opposite direction from what was intended.

Sleep apnea is a disorder in which breathing repeatedly stops and restarts during sleep, often because the muscles at the back of the throat relax too much and block the airway. (A) Doctors therefore rely less on a patient's own account of the night and more on objective measurements, such as overnight oxygen levels and airflow patterns recorded in a sleep laboratory. (B) Each pause can last from a few seconds to over a minute, and it may occur dozens of times in a single night without the sleeper ever waking up fully. (C) Because these interruptions rarely produce a clear memory the next morning, many people remain unaware that anything is wrong, even as chronic fatigue, headaches, and irritability build up over months.

In other words, the body keeps a running total rather than resetting each day. Sleep debt refers to the cumulative gap between the amount of sleep a person needs and the amount they actually get. ( ① ) Unlike a financial debt, however, this deficit cannot simply be repaid with a single long weekend of rest. ( ② ) When someone loses two hours of sleep every night for a week, the body does not treat the shortage as fourteen separate small losses; instead, it accumulates the deficit, and the resulting impairment in attention and mood can resemble that of a person who has been awake for an entire night. ( ③ ) Researchers have found that even modest, chronic sleep restriction gradually impairs reaction time and decision-making, often without the affected person noticing the decline. ( ④ ) This is because subjective feelings of tiredness tend to plateau after a few days, even as objective performance keeps deteriorating. ( ⑤ ) Consequently, people frequently underestimate how much sleep debt they are carrying until a demanding task suddenly exposes the accumulated cost.

This built-in schedule does not simply respond to the clock on the wall; it is shaped directly by light itself. Every cell in the human body follows an internal timer known as the circadian rhythm, a roughly twenty-four-hour cycle that governs when we feel alert and when we feel drowsy. ( ① ) This clock is regulated primarily by a tiny cluster of neurons in the brain that responds to light entering through the eyes. ( ② ) When morning sunlight strikes the retina, the cluster signals the body to suppress sleep hormones and raise body temperature, preparing us for activity. ( ③ ) As evening approaches and light fades, the same mechanism triggers the release of melatonin, a hormone that promotes drowsiness. ( ④ ) Because this rhythm evolved around the natural cycle of day and night, modern habits such as staying indoors under artificial light or working night shifts can push the internal clock out of sync with the external environment. ( ⑤ ) Such misalignment does not simply cause tiredness; it has also been associated with digestive problems and reduced concentration, suggesting that timing matters as much as total sleep hours.