题目内容：
共用题干第二篇
Sleep Necessary for Memories
Burning the midnight oil before an exam or interview does harm to the performance
according to a recent research which found that sleep is necessary for memories to be
taken back into the brain.A good night's sleep within 30 hours of trying to remember a
new task is a required condition of having good recall in the weeks ahead,scientists
have found.
The research,published in the December issue of Nature Neuroscience,showed that
it was the act of sleep,rather than the simple passage of time,that was critical for
long-term memory formation.
"We think that getting that first night's sleep starts the process of memory consolidation
（巩固）,"said Robert Stickgold, a sleep researcher at Harvard Medical School who
conducted the latest study.
"It seems that memories normally wash out of the brain unless some process nails them
down.My suspicion is that sleep is one of those things that does the nailing down,"
Professor Stickgold said.
With about one in five people claiming that they are so chronically short of sleep that it
affects their daily activities,the latest work emphasizes the less well一understood side
effect一serious memory impairment（损害）.
Volunteers in an experiment found it easier to remember a memory task if they were
allowed to sleep that night.But for those kept awake,no amount of subsequent sleep
made up for the initial loss.
Professor Stickgold's team trained 24 people to identify the direction of three diagonal
（斜线形的）bars flashed for a sixtieth of a second on a computer screen full of horizontal
（水平的）stripes.
Half of the subjects were kept awake that night,while the others slept.Both groups
were allowed to sleep for the second and third nights to make up for any differences in
tiredness between the volunteers.
Those who slept the first night were significantly and consistently better at remembering
the task while the second group showed no improvement despite enjoying two nights of
catch-up sleep.
Stickgold's research focused on the side effect produced by
A:memory impairment.
B:lack of sleep.
C:low work efficiency.
D:memory recall.
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