单选题Cigarette smoking is a major health ______ and may result in your death.

单选题 Questions6-8 are based on the conversation you have just heard.

单选题To be ______ I couldn't understand what he was getting at. If you wanted to know you'd better ask someone else. A. sly B. humble C. honest D. cowardly

单选题Christmas Eve is ______.

单选题 Two keen minds that they are, they took ______ each other.

单选题He was ______ to tell the truth even to his closest friend. A. too much of a coward B. too much the coward C. a coward enough D. enough of a coward

单选题Why someone sneezed the writer (Paragraph 11 )?

单选题Weather ______, we wild go on with our journey through the west.

单选题[此试题无题干]

单选题How many Chinese students are involved in the conference?

单选题What is the ______ in going by boat when the plane costs no more and is quicker?(2002年武汉大学考博试题)

单选题Poverty is not ______ in most cities although, perhaps because of the crowded conditions in certain areas, it is more visible there.

单选题--"Did you review your lessons last night?"--"No, but if I ______, I would have done better on today's test."

单选题In this passage, the writer is clearly stating the intention which is to get the reader to ______.

单选题 Birds that are literally half asleep—with one brain hemisphere alert and the other sleeping—control which side of the brain remains awake, according to a new study of sleeping ducks. Earlier studies have documented half brain sleep in a wide range of birds. The brain hemispheres take turns sinking into the sleep stage characterized by slow brain waves. The eye controlled by the sleeping hemisphere keeps shut, while the wakeful hemisphere's eye stays open and alert. Birds also can sleep with both hemispheres resting at once. Decades of studies of bird flocks led researchers to predict extra alertness in the more vulnerable, end-of-the-row sleepers. Sure enough, the end birds tended to watch carefully on the side away from their companions. Ducks in the inner spots showed no preference for gaze direction. Also, birds dozing at the end of the line resorted to single hemisphere sleep, rather than total relaxation, more often than inner ducks did. Rotating 16 birds through the positions in a four duck row, the researchers found outer birds half asleep during some 32 percent of dozing time versus about 12 percent for birds in internal spots. 'We believe this is the first evidence for an animal behaviorally controlling sleep and wakefulness simultaneously in different regions of the brain,' the researchers say. The results provide the best evidence for a long standing supposition that single hemisphere sleep evolved as creatures scanned for enemies. The preference for opening an eye on the lookout side could be widespread, he predicts. He's seen it in a pair of birds dozing side by side in the zoo and in a single pet bird sleeping by a mirror. The mirror side eye closed as if the reflection were a companion and the other eye stayed open. Useful as half sleeping might be, it's only been found in birds and such water mammals (哺乳动物) as dolphins, whales, and seals. Perhaps keeping one side of the brain awake allows a sleeping animal to surface occasionally to avoid drowning. Studies of birds may offer unique insights into sleep. Jerome M. Siegel of the UCLA says he wonders if birds' half brain sleep 'is just the tip of the iceberg (冰山).' He speculates that more examples may turn up when we take a closer look at other species.

单选题Our visual perception depends on the reception of energy reflecting or radiating from ______ which we wish to perceive.

单选题Without water from the Nile River, Egypt ____ a farming country and become a desert.

单选题A girl contemplates ______ a sweater previously worn by her ex-boyfriend, but she finds the garment repulsive.

单选题Whenever he comes across a serious problem, he likes to ______ it, namely, to think it about carefully and for a long time.