问题 不定项选择

一平行板电容器的两个极板水平放置,两极板间有一带电量不变的小油滴,油滴在极板间运动时所受空气阻力的大小与其速率成正比。若两极板间电压为零,经一段时间后,油滴以速率v匀速下降;若两极板间的电压为U,经一段时间后,油滴以速率v匀速上升。若两极板间电压为-U,油滴做匀速运动时速度的大小、方向将是 [ ]

A.2v、向下

B.2v、向上

C.3v、向下

D.3v、向上

答案

答案:C

阅读理解

阅读理解。

    Linda has been a vegetarian for years. She stopped eating meat because of how she felt As she told her

doctor, she always felt tired. Her doctor looked her over and told her to eat less meat She bought a vegetarian

cookbook and decided to "go all the way". She still eats eggs and cheese sometimes; now, however, most of

her food is vegetables, fruits, and grains. Linda became a vegetarian to improve her health. 

    Nancy is an animal lover. Nancy grew up on a farm where there were cows and chickens. As she grew

older, she started to eat less meat. One day she realized that she had stopped eating meat. It had never seemed

right to her that animals were fed to be killed for food.

    When Mark was a student, he had a careful plan of how to spend money. The little money that he had for

food, he spent on rice, cheap vegetables. He learned to be a very good cook. Now Mark is a successful

engineer, but he still eats simple foods, and no meat.

    Roy is an environmentalist. He knows that the population is increasing faster and faster, but the land for

growing food is not increasing at all. He knows that it takes sixteen kilos of grain to make one kilo of meat;

he thinks about the fifteen kilos of grain that are wasted if he eats meat "Somewhere," he says, "someone

hasn't got enough to eat and is dying. How can I enjoy a thick steak?" Mark's ideas about what is right and

wrong make him a vegetarian.

1.According to the passage, a vegetarian usually will not eat ______. [ ]

A.

B.

C.

D.

2.Linda became a vegetarian because ______. [ ]

A.her doctor asked her to do so

B.she was badly ill

C.she enjoyed eating vegetables

D.she wanted to be healthier

3.Mark became a vegetarian ______.[ ]

A.when he was a student

B.after he was able to cook vegetables well

C.after he became an engineer

D.because he thought vegetables were nice

4.Which of the following is true? [ ]

A.Linda only eats fruits and vegetables.

B.We aren't sure when Roy became a vegetarian.

C.Nancy became a vegetarian when she was old.

D.Roy doesn't like steak at all.

5.The main idea of this passage is that ______. [ ]

A.people choose to be vegetarians for different reasons

B.people become vegetarians because they don't like meat

C.meat is not good for one's health

D.we had better become vegetarians

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