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51、根据以下内容，回答51-70题。
Researchers have found that REM (rapid eye movement) sleep is important to human beings．This type of sleep generally occurs four or five times during one night of sleep lasting five minutes to forty minutes for each occurrence．The deeper a person’s sleep becomes, the longer the periods of rapid eye movement．
There are physical charges in the body to show that a person has changed from NREM (non-rapid eye movement) to REM sleep．Breathing becomes faster, the heart rate increases, and, as the name implies, the eyes begin to move quickly．
Accompanying these physical changes in the body is a very important characteristic of REM sleep．It is during REM sleep that a person dreams．
According to the passage, how often does REM sleep occur in one night?
A．Once
B．Twice
C．Four of five times
D．Forty times


52、 The word “deeper” in paragraph 1 is closest in meaning to which of the following?
A．heavier．
B．louder．
C．stronger．
D．happier．


53、 Which of the following shows that a person is NOT dreaming in his sleep?
A．His eyes begin to move．
B．His breathing becomes faster．
C．His heart rate increases．
D．His eyes stop moving．


54、 The subject of this passage is ________．
A．why people sleep
B．the human need for REM sleep
C．the characteristic of REM sleep
D．physical changes in the human body


55、 Which of the following is the best title of the article?
A．REM Sleep
B．Two Types of Sleep
C．Sleepers
D．What Happens to Sleepers


56、 根据以下内容，回答56-75题。
Are you aware that you actually possess six senses? The sixth is a muscular sense responsible for directing your muscles intelligently to the exact extent necessary for each action you perform．For example, when you reach for an object, the sensory nerves linking the muscles to the brain stop your hand at the correct spot．This automatic perception of the position of your muscles in relation to the object is your muscular sense in action．
Muscles are stringly bundles of fibers varying from one five-thousandth of an inch to about three inches．They have three unique characteristics, they can become shorter and thicker; they can stretch; and they can retract to their original positions．Under a high-powered microscope, muscle tissue is seen as long, slender cells with a grainy texture like wood．
More than half of a person’s body is composed of muscle fibers, most of which are involuntary-in other words, work without conscious direction．The voluntary muscles, those that we move consciously to perform particular actions, number more than five hundred．Women have only 60 to 70 percent as much muscle as men for their body mass．That is why an average woman can’t lift as much, throw as far, or hit as hard as an average man．
According to the selection, the muscular sense is responsible for ______．
A．the efficiency of our muscles
B．the normal breathing function
C．directing our muscles intelligently
D．the work of only our involuntary muscles


57、 Intelligent use of the muscles means that ________．
A．one always knows what his muscles are doing
B．one performs simple actions whithout working
C．one’s muscles are used only to the extent necessary for each action they perform
D．one improves muscular action consciously


58、 Muscles are unique fibers because, they can ________．
A．contract
B．stretch
C．retract
D．do all of the above


59、 Under a microscope, muscle cells appear to be _______．
A．textured like wood
B．colored like wood
C．smooth and red
D．short and thick


60、 According to the selection more than half of a person’s body is composed of ______．
A．voluntary muscles
B．involuntary muscles
C．muscle fibers
D．sensory nerves