71. A chronic lack of sleep may result in ____.

1. car accidents
2. all kinds of crashes
3. weak body
4. insomnia

72. Sleep intensity refers to ____.

1. how long one can sleep
2. how well one can sleep
3. how many dreams one has in one's sleep time
4. how sleep helps the brain process memories

73. Fishbein and his graduate student devised a test and found that ____.

1. slow-wave sleep came earlier than a nap
2. brain could put together relational memory
3. the nappers memorized more words than non-nappers
4. even a 12-minute nap can boost some forms of memory

74. Fragmented sleep, according to the research, ____.

1. comes with aging or apnea as a REM sleep
2. keeps new brain cells from growing
3. makes people easy to learn knowledge
4. can be made up by the catch-up sleep

75. Up to now, the researches have drawn certain conclusions EXCEPT ____.

1. how long the minimum sleep is needed for optimal memory
2. sleep apnea can be treated and napping is good for memory
3. a nap may boost a sophisticated kind of memory that helps us get creative
4. one may have a very efficient deep sleep even if he sleeps only four hours

(Reference keys.)