How sleep helps US consolidate memories is still largely a mystery. A recent study from the University of Liibeck, in Germany, offers one clue-Subjects were given a list of 46 word pairs to memorize, just before sleep. Then when they reached the deepest stages of sleep, electrical currents were sent through electrodes on their" heads to induce very slow brain waves. Such slow waves were induced at random in the brains of one group of subjects, but not another. The next morning, the slow-wave group had better recall of the words. Other types of memory were no| improved, and inducing the slow waves later in the night did not have the same eftect. Why and how the slow waves improved memory is not yet understood, but they are thought to alter the strengths of chemical connections, or synapses, between specific pairs of nerve cells in the brain. Memories are "stored" in these synapses: changing the strength of the synapses increases the strength of the memories they store. It's not just memory that is improved by sleep. Recent studies indicate that sleep riot only helps store facts, it also helps make connections between them. Ullrich Wagner arid colleagues in Germany used a puzzle in which players were given a string of numbers, and required to make a series of seven calculations based on these numbers. The seventh calculation (which depended on the preceding six) was the" answer. "Participants repeatedly played the same game with the same roles, but different sets of numbers. The researchers structured the game such that the second calculation always gave the same answer as the seventh calculation-the final answer. If players recognized this rule, they could get to the final answer much faster. Sonic of the players played the game in the morning, then did other things for eight hours or so, then played the game again. Others played the game first in the evening, then slept, then played it again alter awakening. The players who slept were almost three times more likely to have the insight that allowed them to spot the rule. Why is this important? Some sleep researchers believe that for every two hours we spend awake, the brain needs an hour of sleep to figure out what all these experiences mean, and that sleep plays a crucial role in constructing the meaning our lives come to hold. Breakdowns in such sleep-dependent processing may contribute to the development of depression, and may explain why some people who experience horrific traumas go on to develop post-traumatic stress disorder.
单选题
When did slow waves function in the subjects' brains in the experiment?
【正确答案】
B
【答案解析】根据题干关键词show waves定位到第一、二段。第一段第四句说：Then when they reached the deepest stages of sleep. electrical currents were sent through electrodes on their heaths to induce very slow brain waves(当他们进入深度睡眠时，电流通过头上的电极传到大脑中来引起非常缓慢的脑电波)，由此我们可以推断，本题的正确答案为B。第二句中也提到在这个时间之后低速脑电波就不会产生作用了，因此排除了C和D项，而A项文中并没有提及。
单选题
"Synapses" (Line 4, Paragraph 2) can be explained as
【正确答案】
C
【答案解析】分析被考查词汇所在的句子：they are thought to alter the strengths of chemical connections, or synapses，通过并列连词or我们就可以判定前后两个句词是相互解释的天系，因此本题的正确答案为C。
单选题
It is believed that people can remember well after they receive slow waves because
【正确答案】
A
【答案解析】本题的答案仍然出现在第二段第三句：they are thought to alter the strengths of chemical connections, or synapses, between specific pairs of nerve cells in the brain(它们被认为改变了大脑中特定神经细胞对的化学联结点，或者叫脑突触的强度)，A选项与此相符，因此为正确答案。
单选题
Apart from helping store facts, sleep also
【正确答案】
D
【答案解析】第三段第二句说：Recent studies indicate that sleep not only helps store facts. it also helps make connections between them(最近的研究表明睡眠不仅帮助储存事实信息，还帮助在这些事实间寻找联系)，因此本题的正确答案为D。其他三个选项在文中都没有提及。