영어 모의고사 (자동 편성)

Every cell in the human body follows an internal timer known as the circadian rhythm, a roughly twenty-four-hour cycle ①that governs when we feel alert and when we feel drowsy. This clock is regulated primarily by a tiny cluster of neurons in the brain ②that responds to light entering through the eyes. When morning sunlight strikes the retina, the cluster signals the body ③to suppress sleep hormones and raise body temperature, preparing us for activity. As evening approaches and light fades, the same mechanism triggers the release of melatonin, a hormone ④promotes drowsiness. 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. Such misalignment does not simply cause tiredness; it has also ⑤been associated with digestive problems and reduced concentration, suggesting that timing matters as much as total sleep hours.

Sleep debt refers to the cumulative gap between the amount of sleep a person needs and the amount they actually get. Unlike a financial debt, however, this deficit cannot simply ①be repaid with a single long weekend of rest. 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 ②who has been awake for an entire night. Researchers have found that even modest, chronic sleep restriction gradually impairs reaction time and decision-making, often without the affected person ③noticing the decline. This is because subjective feelings of tiredness tend to plateau after a few days, even as objective performance keeps ④deteriorate. Consequently, people frequently underestimate how much sleep debt they are carrying until a demanding task suddenly ⑤exposes the accumulated cost.

Rather than displaying products in the usual manner, the team designed the space to resemble a colorful garden, inviting visitors to explore and take photographs. Lines formed outside the store within days, even though the products themselves were already available online. Curious about this success, a marketing researcher later interviewed several visitors, who explained that the temporary nature of the event made the experience feel special and worth attending in person. When the two weeks ended, the brand reported a significant ①decrease in both sales and social media followers. ②Encouraged by these results, the company ③began planning ④additional pop-up events in ⑤other cities.

Have you ever felt a ①boring class lasted forever while an exciting weekend disappeared in an instant? This common experience reflects what psychologists call the distortion of time perception: subjective time can differ from actual clock time. Researchers explain that people who focus intensely on an enjoyable activity process fewer separate moments, so time seems to pass ②slowly. In contrast, bored or anxious people pay ③closer attention to each moment, making time feel as though it is dragging. When people become deeply ④engaged in a task, they often lose track of time, unaware of how many minutes have passed. For example, athletes and musicians often say that hours felt like minutes while they were fully ⑤absorbed in performance.

After a strenuous workout, muscle fibers experience thousands of ①microscopic tears, and the body immediately begins a repair process that ultimately makes the muscle stronger than it was before. This repair depends heavily on amino acids, the building blocks that protein supplies, which is why sports scientists recommend consuming protein within a couple of hours after training. Waiting too long to eat can ②slow recovery, since a muscle's sensitivity to amino acids gradually declines once that window closes. Many athletes assume that eating an enormous quantity of protein in a single sitting will ③delay this process, but the body can only use a limited amount at once; the rest is simply burned for energy or stored as fat. For this reason, nutritionists generally advise spreading moderate portions of protein ④evenly across several meals throughout the day rather than saving it all for one large post-workout ⑤meal.

Aerobic exercise strengthens the heart by forcing it to pump larger volumes of blood with each beat. 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. This adaptation explains why _______________. Beyond the heart itself, aerobic activity also builds new capillaries within muscle tissue and improves how cells throughout the body respond to insulin.

Smartphones, tablets, and computer screens all emit a significant amount of blue light, a short-wavelength light that our eyes are especially sensitive to. (A) At night, however, the same wavelength can interfere with the body's natural preparation for sleep by suppressing the release of melatonin. (B) During the day, exposure to blue light from the sun helps keep us alert and mentally sharp, which is generally beneficial. (C) For this reason, some devices now offer a night mode that shifts the display toward warmer tones, though sleep researchers still recommend limiting screen use before bedtime.

Athletes preparing for major endurance events sometimes train for weeks at high altitude, where the air contains less oxygen than at sea level, in hopes of gaining a physiological edge once they return to compete at lower elevations. (A) Many elite programs therefore follow a strategy known as live high, train low, balancing the benefits of altitude exposure against the need for high-quality workouts. (B) In this thin air, the body responds by producing more red blood cells, which carry oxygen more efficiently through the bloodstream to working muscles. (C) However, the benefits of altitude training are far from guaranteed, since individual athletes respond quite differently to the same conditions, and some experience excessive fatigue that undermines the very training they hoped to complete.

This is precisely why an experienced athlete returning after an injury often regains sharp form faster than a complete beginner ever could. Anyone who has ridden a bicycle after a decade away from one has likely experienced muscle memory firsthand: the body seems to recall a complex skill almost instantly, even when conscious memory of the exact movements has faded. ( ① ) Contrary to what the name suggests, muscles themselves do not actually store memories; the phenomenon originates in the brain and nervous system, where repeated practice gradually shifts control of a well-learned movement from regions associated with conscious thought to areas that operate largely automatically. ( ② ) This shift explains why a skilled athlete can execute a complicated sequence of movements without consciously thinking through each individual step, freeing mental attention for strategy and decision-making instead. ( ③ ) Interestingly, research also suggests that these neural pathways can remain partially intact even after long periods without practice, which is why relearning a skill is typically much faster than learning it for the very first time. ( ④ ) Coaches often exploit this principle by ensuring that fundamental techniques are practiced correctly from the very beginning. ( ⑤ )

This grogginess occurs because the brain has not fully completed a sleep cycle and is abruptly pulled out of its deepest phase. A short nap taken in the early afternoon, often called a power nap, can noticeably sharpen attention and mood without leaving a person groggy afterward. ( ① ) The key lies in timing: naps limited to roughly twenty minutes allow the brain to pass through the lightest stages of sleep while avoiding the deeper stages associated with slow-wave activity. ( ② ) If a nap extends much beyond that window, the sleeper risks waking during deep sleep, which produces a foggy, disoriented feeling known as sleep inertia that can persist for thirty minutes or more. ( ③ ) Laboratory studies comparing napping and non-napping groups have repeatedly shown that a brief nap improves reaction time and short-term memory almost as effectively as a full night of extra rest. ( ④ ) Interestingly, the benefit appears strongest when the nap occurs several hours after waking, since this is when the body's natural dip in alertness makes rest most effective. ( ⑤ ) For this reason, many workplaces now designate quiet rooms where employees can recharge briefly during the day.