单选题(　　)there is fresh air, there is oxygen.

单选题Trees are useful to man in three important ways: they provide him with wood and other products; they give him shade; and they help to prevent droughts and floods. Unfortunately, in many parts of the world, man has not realized that the third of these services is the most important. In his eagerness to make money from trees, he has cut them down in large numbers, only to find that without them he has lost the best friends he had. And besides, he is usually too careless to plant and look after new trees. So the forests slowly disappear. This does not only mean that man will have fewer trees. The results are even more serious: for where there are trees, their roots break up soil—allowing the rain to sink in—and also bind the soil, thus preventing it from being washed away easily; but where there are no trees, the rain falls on hard ground and flows away, causing floods and carrying away the rich top-soil. When all the top-soil is gone, nothing remains but worthless desert. Two thousand years ago a rich and powerful country cut down its trees to build warships, with which to gain itself an empire. It set up the empire but, without its trees, its soil became poor and it grew weak. When the empire fell to pieces; the home country found itself faced with floods and starvation.

单选题I know nothing about the young lady ______ she is from Beijing.

单选题Her excellent performance made a deep __________ on the audience．

单选题In this factory, suggestions often have to wait for months before they are fully ___.

单选题He spoke English so well that I took it ______ that he was an American.

单选题Susan wants to know whether the measures have been agreed ______ A. to B. with C. over D. upon

单选题Good use must be ______ the computer which is now sitting idle.

单选题Anyone, rich or poor, old or young, sick or ______ can follow a favorite hobby.

单选题Mark: Let"s go and sit down for a while. I need to rest and have a drink. Lima: ______. I"m tired too.

单选题I wrote him a letter to show my ______ of his thoughtfulness.

单选题(By reading) the directions (carefully), some mistakes (in the exam) could (have been) avoided.

单选题(As) a slow student, Jane (hasn"t finished) her test (in time), (is she)?

单选题The theory is of great importance _______ the hotter a boby is, the more energy it radiates.

单选题You"re ______ understand the real meaning of love.

单选题The room is in a terrible mess; it ______ cleaned. A. can't have been B. mustn't have been C. shouldn't have been D. wouldn't have been

单选题Without computers, much of the advanced technology ______.