영어 모의고사 (자동 편성)

Melatonin is a hormone ① 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, ② 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 ③ 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, melatonin does not force sleep to occur; instead, it signals to the rest of the body that night has arrived, ④ 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 ⑤ intending.

Browsing an online store today often means chatting with an AI assistant that asks a few quick questions, such as budget or intended use, before suggesting a short list of products ① tailored to the answers. Unlike a static list of best-sellers, this assistant can adjust its suggestions on the spot, responding to follow-up questions the way a knowledgeable salesperson might in a physical store. Retailers report that shoppers who use these chatbots tend to ② complete purchases more often and return fewer items, since the guided conversation helps buyers choose products that actually fit their needs. Some shoppers, however, remain ③ confident about how personal the questions can feel, wondering how much of that conversation is quietly stored and reused to influence future purchases. Consumer advocates argue that stores should ④ clearly explain what happens to this data, rather than ⑤ burying the explanation in a lengthy privacy policy that almost no one reads.

Even a modest level of dehydration, as little as two percent of body weight lost through sweat, can measurably ① increase an athlete's endurance and cognitive sharpness during competition. As fluid levels drop, blood volume decreases, forcing the heart to work harder to deliver the same amount of oxygen to working muscles, which ② accelerates fatigue. Dehydration also impairs the body's ability to regulate its own temperature, since sweating is the primary mechanism for releasing excess heat during intense exercise. Athletes competing in hot, humid conditions face a particularly ③ difficult balance, because sweating heavily to stay cool simultaneously depletes the very fluids needed to sustain performance. Simply drinking large amounts of plain water is not always sufficient, however, since heavy sweating also flushes out sodium and other electrolytes ④ essential for proper muscle function. For this reason, sports scientists generally recommend a hydration strategy that replaces both fluid and electrolytes, ⑤ tailored to an individual athlete's sweat rate and the specific conditions of the event.

When people consistently sleep too little, the body's hormonal balance shifts in ways that can ① quietly encourage weight gain. Two hormones in particular play ② 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 a tired body ends up feeling ③ fuller than it actually needs to be, even after a normal-sized meal. At the same time, insufficient sleep interferes with how efficiently the body processes glucose, making cells less ④ 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 ⑤ 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.

Cities are frequently several degrees warmer than the surrounding countryside, a phenomenon known as the urban heat island effect, which intensifies in summer and threatens public health. This disparity arises largely because asphalt and concrete absorb solar radiation during the day and slowly release it as heat throughout the night, preventing urban areas from cooling down. Furthermore, the scarcity of vegetation in densely built areas removes a natural cooling mechanism, since plants lower temperatures by evaporating water from their leaves. To address this problem, urban planners _______________. One widely used solution involves reflective "cool" roofing engineered to reflect more sunlight than dark rooftops absorb. Another strategy, green infrastructure, incorporates rooftop gardens and tree-lined streets that provide shade while releasing moisture. In contrast, some cities have pursued permeable pavements that let water seep through and evaporate, cooling nearby surfaces. Collectively, these strategies show that reducing urban heat depends on combining approaches suited to a city's geography.

Scientists have identified certain gene variants that appear more frequently among elite endurance athletes than among the general population, along with a separate set that seems to favor explosive, power-based sports such as sprinting. One frequently studied variant, for instance, influences the proportion of slow-twitch versus fast-twitch muscle fibers a person naturally develops, a ratio that shapes whether a body leans toward endurance or explosive power. However, researchers caution strongly against interpreting these findings as evidence that athletic greatness is simply inherited, since _______________. Genetics may set a rough ceiling on an individual's ultimate potential, but where any particular athlete lands within that range depends overwhelmingly on training quality, nutrition, coaching, and sheer determination.

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.

Open a music streaming app on any given morning, and a personalized playlist is usually already waiting, assembled overnight from songs the algorithm predicts will match a listener's current mood. (A) Musicians, meanwhile, have mixed feelings about this shift, since a song the algorithm decides not to promote may struggle to reach listeners no matter how well it was written. (B) Listeners often praise the feature for introducing them to artists they never would have searched for on their own, effectively acting as a tireless music scout working around the clock. (C) This prediction relies on far more than genre alone; the system studies skip rates, replay counts, and even the time of day a song is typically played to build a detailed profile of individual taste.

Long before humans learned to drill for oil, microorganisms had already mastered the art of converting sunlight and carbon dioxide into stored chemical energy. (A) Modern biofuel research borrows this ability, cultivating algae or engineered bacteria in large tanks where they can be coaxed into producing oils and sugars that can be refined into fuel usable in existing engines. (B) Unlike crops grown for corn-based ethanol, which compete directly with food production for arable land, many algae strains can thrive in shallow ponds, wastewater, or even coastal seawater unsuitable for conventional agriculture. (C) Engineers have also learned to boost oil yield through genetic tinkering, yet producing biofuel at a cost competitive with fossil fuel remains difficult, since harvesting and processing the organisms consumes a substantial share of the energy the fuel itself will eventually provide.

Static stretching, in which a muscle is held at its longest length for an extended period, can actually reduce the muscle's ability to generate explosive force immediately afterward. For decades, athletes were taught to stretch a muscle and hold the position before any competition, believing that this practice alone would prevent injury. ( ① ) Recent research, however, has complicated that assumption considerably. ( ② ) This is especially troubling for sprinters or jumpers who need maximum power right away. ( ③ ) Dynamic stretching, which involves controlled, repeated movement through a joint's full range of motion, appears to prepare muscles for activity without this temporary weakening effect. ( ④ ) As a result, many coaches now recommend saving static stretching for after a workout, while reserving dynamic movements for the warm-up period before intense effort begins. ( ⑤ )