单选题 All mammals require sleep; it is an essential part of life. For giraffes, two hours a
Line day is enough. For bats, that number is closer to twenty. The average adult human
needs between seven and nine hours of sleep every day. Despite these differences,
mammals all have one thing in common: If they do not get enough sleep, they can
(5) suffer serious mental and physical consequences.
The most extensive sleep research has been conducted on people. Through
these studies, scientists have identified two broad categories of sleep, which can
be further divided into five stages with distinct physiological functions. Taken
together, they form a complete sleep cycle. The first four stages are marked by a
(30) lack of rapid eye movement (REM). Therefore, they are referred to as non-REM
sleep. While people are engaged in non-REM sleep, several things are occurring.
Researchers have discovered that during this early sleep, the human body
releases a series of hormones responsible for the proper functioning of certain
body systems. Disrupted sleep can cause these hormones to fall out of balance.
(15) The results can contribute to disorders such as diabetes, depression, infertility,
or even cancer. Lack of sleep, especially in stages 3 and 4, can literally stunt the
growth of children and may increase rates of obesity in adults.
Stage 5 sleep is defined by the occurrence of rapid eye movement, otherwise
known as dreaming. Note that, while REM sleep is the final stage in a sleep cycle,
(20) a complete cycle generally lasts only about 95 minutes. A person will experience
four to six cycles in one sleep session, with REM sleep taking up a larger portion
of the cycle as the night continues. Scientists have advanced several theories
about why humans need REM sleep. One view is that dreaming aids in memory
consolidation. Under this theory, during REM sleep the brain not only strengthens
(25) memory of important actions or events, but it weakens memory of unimportant
things. Another view is that dreaming is necessary for proper central nervous
system development. Yet another theory suggests that REM sleep involves the
repair of monoamine receptors. The theories are not necessarily exclusive; in fact,
they all reach the conclusion that REM sleep deprivation can result in death.

单选题 The author of the passage is primarily concerned with

单选题 The author implies that disrupted sleep can cause disorders such as diabetes (line 15) because

【正确答案】 D

【答案解析】This is an implication question, so the correct answer will be strongly supported by the information in the passage. Answer choice D makes explicit the implied link between hormone production and disorders such as diabetes. While obesity and diabetes have been linked, the connection is not made in this passage, so answer choice A is incorrect. Answer choice B is contradicted by the passage. Answer choice C simply restates the question; it does not address the reasons why. Answer choice E is outside the scope of the passage.

单选题 The passage suggests that the author would be most likely to agree with which of the following statements?

单选题 The author's argument is developed primarily by the use of

【正确答案】 E

【答案解析】Tone is essential to answering this question; the correct answer choice must have a neutral tone. Answer choices A and B are not neutral; in addition, they are incorrect because specific studies are not mentioned in the passage. While the passage does warn against getting too little sleep, this is not how the argument is developed. Therefore, answer choice C is incorrect. Answer choice D is incorrect because the author does not develop an opinion about non-human sleep. Only answer choice E correctly captures the tone and scope of the passage.