영어 모의고사 (자동 편성)

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

Sleep hygiene refers to a set of simple daily habits that ①helps the body prepare for consistent, restorative rest. Experts commonly recommend going to bed and waking up at the same time every day, even on weekends, because an irregular schedule confuses the body's internal clock and makes it ②harder to fall asleep on demand. They also advise reserving the bedroom for sleep alone, since using the bed to study, scroll through a phone, or watch videos teaches the brain ③to associate that space with wakeful activity rather than rest. Physical environment matters as well: a cool, dark, and quiet room tends ④to produce deeper sleep than one that is warm, bright, or noisy. None of these individual habits guarantees a good night's sleep on its own, but together they form a routine that gradually trains the body to expect and enter sleep more easily, much the way a consistent set of cues trains an athlete's body ⑤to perform at a certain time each day.

Travelers who cross several time zones in a single flight often arrive feeling ①exhausted, foggy, and strangely out of sync with the local clock. The discomfort arises because the body's internal clock, which governs sleep, hunger, and alertness, continues to run on the schedule of the departure city even after landing. ②Realigning 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 ③severe symptoms than flying westward, because advancing the internal clock forward is generally harder for the body than delaying it. Exposure to natural light at the right moments after arrival can help ④speed up the adjustment, since light is the strongest external cue the internal clock uses to reset itself. Without such adjustments, travelers may continue to experience disrupted sleep and reduced concentration for ⑤several minutes after a long international flight.

Economists traditionally measured a community's wealth in terms of factories, income, or infrastructure, yet sociologists increasingly point to a less visible resource: social capital, the networks of trust and reciprocity that allow people to cooperate for mutual benefit. Robert Putnam popularized the concept by documenting a decline in civic participation, a trend he captured in the phrase bowling alone. Communities rich in social capital tend to enjoy lower crime and more effective local government, because neighbors who know and trust one another can coordinate informally without relying entirely on formal institutions. However, _______________. For this reason, researchers increasingly distinguish between bonding capital, which strengthens ties within a single group, and bridging capital, which connects otherwise separate communities.

When people consistently sleep too little, the body's hormonal balance shifts in ways that can quietly encourage weight gain. Two hormones in particular play opposing roles in regulating appetite: leptin signals fullness to the brain, while ghrelin stimulates the sensation of hunger. Studies show that sleep deprivation lowers leptin levels while raising ghrelin levels, so _______________, even after a normal-sized meal. At the same time, insufficient sleep interferes with how efficiently the body processes glucose, making cells less responsive to insulin and leaving more sugar circulating in the bloodstream than usual. Over months or years, this combination of increased appetite and reduced insulin sensitivity can contribute to steady weight gain and raise the risk of developing type 2 diabetes. Because these effects build up so gradually, many people never connect their shifting eating habits or worsening blood sugar to something as ordinary as a few lost hours of sleep each night.

A single fertilized egg eventually gives rise to every cell type in the human body, from neurons to bone, a feat that has fascinated biologists for more than a century. (A) Because harvesting these cells traditionally required destroying a human embryo, the research provoked ethical objections fierce enough to slow funding and legislation in several countries for years. (B) A breakthrough arrived when scientists discovered that ordinary adult skin cells could be reprogrammed into a state resembling embryonic versatility without ever touching an embryo, opening a path for stem cell research that far more scientists and funding agencies are now willing to support. (C) Embryonic stem cells retain much of that original versatility, capable in principle of developing into almost any tissue, which is why researchers have long viewed them as a promising raw material for repairing damaged organs.

Melatonin is a hormone produced by a small gland deep within the brain, and its release follows a remarkably predictable daily pattern. (A) 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. (B) 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. (C) Unlike some hormones that directly cause the body to perform a task, melatonin does not force sleep to occur; instead, it signals to the rest of the body that night has arrived, 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.

A growing number of health apps now track steps, sleep, and heart rate throughout the day, quietly building a detailed picture of a user's physical condition without requiring a single visit to a doctor's office. (A) Doctors caution, however, that these apps are designed to detect patterns, not to diagnose illness, and that a worried user should always confirm any alarming reading with a professional. (B) For people living far from specialists or unable to afford frequent checkups, this kind of constant monitoring can feel like a genuine safety net. (C) By comparing this stream of data against patterns drawn from millions of other users, the app's algorithm can flag early warning signs, such as an irregular heartbeat, long before the person notices anything unusual.

Some researchers worry that casual users may misinterpret a single unusual reading as a serious problem, leading to needless anxiety rather than useful insight. Modern sports wearables, from wrist-worn fitness trackers to smart insoles embedded in running shoes, continuously collect data that would once have required a laboratory to measure. ( ① ) Heart rate, sleep quality, running cadence, and even subtle changes in gait can now be monitored during ordinary daily activity rather than only in a controlled clinical setting. ( ② ) Coaches use this constant stream of information to detect early warning signs of overtraining, sometimes noticing a decline in performance before the athlete consciously feels tired. ( ③ ) However, the flood of data has created a new challenge: distinguishing a meaningful pattern from ordinary daily fluctuation requires expertise that many amateur athletes simply do not have. ( ④ ) For this reason, most experts recommend treating wearable data as a general trend to observe over time, not as a precise diagnostic tool. ( ⑤ )

This process, though it may sound simple, triggers a remarkable series of adaptations throughout the cardiovascular system. Aerobic exercise, such as jogging, swimming, or cycling at a steady pace, strengthens the heart by forcing it to pump larger volumes of blood with each beat. ( ① ) Over weeks of consistent training, the heart gradually enlarges and becomes more efficient, meaning it can deliver the same amount of oxygen to working muscles while beating fewer times per minute. ( ② ) This adaptation explains why trained athletes often have a much lower resting heart rate than sedentary individuals of the same age. ( ③ ) Beyond the heart itself, aerobic activity encourages the body to build new capillaries within muscle tissue, improving the delivery of oxygen and nutrients at a cellular level. ( ④ ) Researchers have also found that regular aerobic exercise reduces inflammation throughout the body and improves the way cells respond to insulin. ( ⑤ )