问题 选择题

关于功率以下说法中正确的是(  )

A.据 P=W/t可知,机器做功越多,其功率就越大

B.据 P=Fv可知,汽车牵引力一定与速度成反比

C.据 P=W/t可知,知道时间t内机器所做的功,就可以求得这段时间内任一时刻机器做功的功率

D.根据 P=Fv可知,发动机功率一定时,交通工具的牵引力与运动速度成反比

答案

A、据

.
P
=
W
t
可知,相同时间内,机器做功越多,其功率就越大,故A错误;

B、据 P=Fv可知,当功率恒定时,牵引力与速度成反比,故B错误;

C、据

.
P
=
W
t
可知,知道时间t内机器所做的功,就可以求得这段时间内做功的平均功率,故C错误;

D、根据 P=Fv可知,发动机功率一定时,交通工具的牵引力与运动速度成反比,故D正确;

故选D.

选择题
阅读理解

     We have met the enemy, and he is ours. We bought him at a pet shop. When monkey-pox,a disease

usually found in the African rain forest, suddenly turns up in children in the American Midwest, it's hard

not to wonder if the disease that comes from foreign animals is homing in on human beings. "Most of the

infections(感染) we think of as human infections started in other animals, "says Stephen Morse, director

of the Center for Public Health Preparedness at Columbia University.    

     It's not just that we're going to where the animals are; we're also bringing them closer to us. Popular

foreign pets have brought a whole new disease to this country. A strange illness killed Isaksen's pets, and

she now thinks that keeping foreign pets is a bad idea. "I don't think it's fair to have them as pets when we have such a limited knowledge of them, "says Isaksen.    

     "Laws allowing these animals to be brought in from deep forest areas without stricter control need

changing," says Peter Schantz. Monkey-pox may be the wake-up call. Researchers believe infected

animals may infect their owners. We know very little about these new diseases. A new bug(病毒) may

be kind at first. But it may develop into something harmful(有害的).            

     Monkey-pox doesn't look a major infectious disease. But it is not impossible to pass the disease from

person to person.

1. We learn from Paragraph l that the pet sold at the shop may___________.    

A. come from Columbia    

B. prevent us from being infected    

C. enjoy being with children    

D. suffer from monkey-pox

2. Why did Isaksen advise people not to have foreign pets?    

A. They attack human beings.    

B. We need to study native animals.    

C. They can't live out of the rain forest.    

D. We do not know much about them yet.

3. What does the phrase "the wake-up call " in Paragraph 3 most probably mean?    

A. a new disease    

B. a clear warning    

C. a dangerous animal    

D. a morning call

4. The text suggests that in the future we           .    

A. may have to fight against more new diseases    

B. may easily get infected by diseases from dogs    

C. should not be allowed to have pets    

D. should .stop buying pets from Africa