单选题--Nice to see you. I ______ you for a long time. --I ______ in Berlin. I've just got back. A. didn't see, am B. wasn't seeing, am C. hadn't see, have been D. haven't seen, was

单选题 Blood vessels running all through the lungs carry blood to each air sac (囊), or alveolus(肺泡), and then back again to the heart. Only the thin wall of the air sac and the thin wall of a capillary (毛细血管) are between the air and the blood. So oxygen easily diffuses from the air sacs through the walls into the blood, while carbon dioxide easily diffuses from the blood through the walls into the air sacs. When blood is sent to the lungs by the heart, it has come back from the cells in the rest of the body. So the blood that goes into the wall of an air sac contains much dissolved carbon dioxide but very little oxygen. At the same time, the air that goes into the air sac contains much oxygen but very little carbon dioxide. You have learned that dissolved materials always diffuse from where there is more of them to where there is less. Oxygen from the air dissolves in the moisture on the lining of the air sac and diffuses through the lining into the blood. Meanwhile, carbon dioxide diffuses from the blood into the air sac. The blood then flows from the lungs back to the heart, which sends it out to all other parts of the body. Soon after air goes into an air sac, it gives up some of its oxygen and takes in some carbon dioxide from the blood. To keep diffusion going as it should, this carbon dioxide must be gotten rid of. Breathing, which is caused by movements of the chest, forces the used air out of the air sacs in your lungs and brings in fresh air. The breathing muscles are controlled automatically so that you breathe at the proper rate to keep your air sacs supplied with fresh air. Ordinarily, you breathe about twenty-two times a minute. Of course, you breathe faster when you are exercising and slower when you are resting. Fresh air is brought into your lungs when you breathe in, or inhale(吸入), while used air is forced out of your lungs when you breathe out, or exhale. Some people think that all the oxygen is taken out of the air in the lungs and that what we breathe out is pure carbon dioxide. But these ideas are not correct. Air is a mixture of gases that is mostly nitrogen (氮). This gas is not used in the body. So the amount of nitrogen does not change as air is breathed in and out. But while air is in the lungs, it is changed in three ways: (1) About one-fifth of the oxygen in the air goes into the blood. (2) An almost equal amount of carbon dioxide comes out of the blood into the air. (3) Moisture from the linings of the air passages and air sacs evaporates until the air is almost saturated.

单选题The same factors push wages and prices up together, the one ______ the other. A. emphasizing B. reinforcing C. multiplying D. increasing

单选题Most people think of lions as strictly African beasts, but only because they"re been killed off almost everywhere else. Ten thousand years ago lions spanned vast sections of the globe. Now lions hold only a small fraction of their former habitat, and Asiatic lions, a subspecies that split from African lions perhaps 100,000 years ago, hang on to an almost impossibly small slice of their former territory. India is the proud steward of these 300 or so lions, which live primarily in a 560-square-mile sanctuary (保护区). It took me a year and a half to get a permit to explore the entire Gir Forest—and no time at all to see why these lions became symbols of royalty and greatness. A tiger will hide in the forest unseen, but a lion stands its ground, curious and unafraid—lionhearted. Though they told me in subtle ways when I got too close, Gir"s lions allowed me unique glimpses into their lives during my three months in the forest. It"s odd to think that they are threatened by extinction; Gir has as many lions as it can hold—too many, in fact. With territory in short supply, lions move about near the boundary of the forest and even leave it altogether, often clashing with people. That"s one reason India is creating a second sanctuary. There are other pressing reasons: outbreaks of disease or natural disasters. In 1994 a serious disease killed more than a third of Africa"s Serengeti lions—a thousand animals—a fate that could easily happen to Gir"s cats. These lions are especially vulnerable to disease because they descend from as few as a dozen individuals. "If you do a DNA test, Asiatic lions actually look like identical twins," says Stephen O"Brien, a geneticist (基因学家) who has studied them. Yet the dangers are hidden, and you wouldn"t suspect them by watching these lords of the forest. The lions display vitality, and no small measure of charm. Though the gentle intimacy of play vanishes when it"s time to eat, meals in Gir are not necessarily frantic affairs. For a mother and her baby lion sharing a deer, or a young male eating an antelope (羚羊), there"s no need to fight for a cut of the kill. The animals they hunt for food are generally smaller in Gir than those in Africa, and hunting groups tend to be smaller as well.

单选题When we were in the mountains, we often found ourselves entirely enveloped by the fog.

单选题Many countries have conservation programs to prevent certain ______ of fish from becoming extinct.

单选题In paragraph 3 the writer uses the phrase "to the best of my knowledge..." because ______.

单选题The information used by the computer to make its detailed maps ______. Ⅰ. was gathered by the Defense Department and the U. S. Geological Survey Ⅱ. shows points roughly 200 feet apart Ⅲ. involves altitude measurements

单选题Some criminal slang is so highly developed that pickpockets, for example, can ______ a conversation in front of a victim without the person's realizing that they are discussing.

单选题Over the last two years, in the PC business Michael Dell has been beaten like a rented mule. His company continues to lose market 25 particularly in the U.S. Industry analysts would say that Dell has done a poor job of bringing out 26 and attractive products. Apple Mac sales keep rising. HP, Sony, and Lenovo have 27 new product lines which have had warm 28 . Dell's core business is being hit by three things. The first is that the company was fairly late at 29 into retail outlets (零售店) overseas. It 30 on its direct sales model for too long. The second problem is that the recession has 31 Dell's sales. Dell's final problem is that it cannot find the right people to run the company. It 32 dumped most of the senior management that it hired just over a year ago. It takes time for new people to get up to speed. Word has gotten out that Dell plans to launch its own high-end smartphone. Dell does not do well what it is supposed to do well. It has become a second rate PC company. It proposes to partially offset that by entering a business which is controlled by Apple and RIM, the maker of the Blackberry. Because smartphone margins are high, Nokia, the world largest cellphone company, Samsung, and Sony Ericsson are also 33 into the market. The traffic jam is going to be 34 . So Dell can't win in the handset business. What it ought to do is to try to improve its PC business. A. receptions E. targeting I. comprehensive M. expanding B. depended F. innovative J. recently N. consequently C. share G. launched K. rushing O. cut D. extraordinary H. declined L. expressions

单选题I got a new battery for my recorder only last week, but it seems to have ______ already. A. worn out B. run down C. knocked off D. gone off

单选题There could have been a war over it but in the end reason______.

单选题Their experiment________，Tom and Mary set out to write the report on the results. 

单选题The doctor ______my forehead and said, "Your forehead ______hot."

单选题So small ______ that the most powerful microscopes cannot detect them. A. are these particles B. were these particles C. these particles are D. these particles were

单选题She ______ much more accurate responses now, had she taken more pains in devising the questions.

单选题A loud noise ______ my attention from cooking and everything was burnt.

单选题Despite his ______ as a trouble-maker, he was promoted to department manger.

单选题Something that is __________ is so bad or unpleasant that it makes you feel disgust or dismay. A. appealing B. appalling C. apparent D. appearing