单选题 The business practices of America will have you in the office from nine in the morning to five in the evening, if not longer. Much of the world, though, prefers to take a nap. And research presented to the AAAS (American Academy of Arts and Sciences) meeting in San Diego suggests it may be right to do so. Matthew Walker and his colleagues at the University of California, Berkeley, have found that they probably have better memory, too. A post-meal snooze, Dr Walker has discovered, sets the brain up for learning. The role of sleep in consolidating memories that have already been created has been understood for some time. Dr Walker has been trying to extend this understanding by looking at sleep's role in preparing the brain for the formation of memories in the first place. He was particularly interested in a type of memory called episodic memory, which relates to specific events, places and times. This contrasts with procedural memory, of the skills required to perform some sort of mechanical task, such as driving. The theory he and his team wanted to test was that the ability to form new episodic memories deteriorates with increasing wakefulness, and that sleep thus restores the brain's capacity for efficient learning. They asked a group of 39 people to take part in two learning sessions, one at noon and one at 6pm. On each occasion the participants tried to memorize and recall 100 combinations of pictures and names. After the first session they were assigned randomly to either a control group, which remained awake, or a nap group, which had 100 minutes of monitored sleep. Those who remained awake throughout the day became worse at learning. Those who napped, by contrast, actually improved their capacity to learn, doing better in the evening than they had at noon. These findings suggest that sleep is clearing the brain's short-term memory and making way for new information. The benefits to memory of a nap, says Dr Walker, are so great that they can equal an entire night's sleep. He warns, however, that napping must not be done too late in the day or it will interfere with night-time sleep. Moreover, not everyone awakens refreshed from a nap. The dazedness that results from an unrefreshing nap is termed "sleep inertia". Sara Mednick, from the University of California, San Diego, suggests that non-habitual nappers suffer from this more often than those who snooze regularly. It may be that those who have a tendency to wake up dazed are choosing not to nap in the first place. Perhaps, though, as in so many things, it is practice that makes perfect.

单选题 Dr. Walker has been trying to find out _____.

单选题 According to Paragraph 3, participants _____.

单选题 What is true about the relationship between sleep and memory?

单选题 Dr. Walker would most probably agree that _____.

单选题 By saying "it is practice that makes perfect" (Line 7, Para. 4), the author means that _____.