2. 外语
  3. All mammals require sleep; it is an essential part of life. For giraffes, two hours a Line day is enough. For bats, that number

All mammals require sleep; it is an essential part of life. For giraffes, two hours a Line day is enough. For bats, that number

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问题       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.
The author’s argument is developed primarily by the use of
选项 A、an attack on poorly constructed sleep research studies
B、a critique of recent scientific studies on REM-sleep
C、a warning against getting too little sleep
D、an analogy between human and non-human sleep processes
E、an overview of specific processes that may occur during different stages of sleep in humans
答案E
解析
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