问题 多项选择题

SF6是化学元素S2和F合成的一种化学气体,比空气重5倍,是无色、无臭、不燃的惰性气体。它作熄弧绝缘有的优点。()

A.SF6气体不存在自由电子,所以绝缘性能良好

B.SF6气体存在自由电子,所以绝缘性能良好

C.灭弧能力比空气大100倍

D.灭弧能力比空气大10倍

答案

参考答案:A, C

阅读理解

阅读理解。

     Many animals do strange things before an earthquake. This news may be important. Earthquakes can

kill people and knock down homes. The animals may help to save lives.

     Some animals make a lot of noise before an earthquake. Farmers have told about this. Dogs that are

usually quiet have started to howl(吠). Horses on farms have run around  in  circles. Mice  have left their

holes and run away. Cows have given less milk.

     In a town in Italy, cats raced down the street in a group. That happened only  a  few hours before an

earthquake. In San Francisco, a man kept tiny(小的) pet frogs. One Sunday, the frogs  jumped  around

more than ever. They made loud noises, like bigger frogs. That night, an  earthquake  struck(袭击)  the

city.

     People want to know when an earthquake is coming. Then  they  could  get away safely. Right  now,

there is no sure way to know ahead of time. Maybe the best way is to watch the animals.

1. This story is mostly about ______________.

A. how animals act before an earthquake  

B. how an earthquake starts

C. home mice leave their homes        

D. when an earthquake begins

2. Before an earthquake, quiet dogs ________________.

A.ran away  

B. started to howl  

C. climbed trees  

D. became quiet

3. Before an earthquake, the frogs ________________.

A. sang    

B. left their homes  

C. jumped around a lot  

D. became quiet  

4. There have been earthquakes in __________.

A. most countries        

B. Italy and San Francisco  

C. Chicago and Spain      

D. all the Western countries

5. People want to _______________.

A. be in earthquake        

B. find out early about an earthquake

C. run around in circles    

D. get away from earthquakes

单项选择题 B1型题