问题 选择题

在如图的闭合电路中,当滑片P向右移动时,两电表读数的变化是(  )

A.

变大,

变大

B.

变小,

变大

C.

变大,

变小

D.

变小,

变小

答案

当滑片P向右移动时,变阻器接入电路的电阻增大,外电路总电阻增大,根据闭合电路欧姆定律得知,总电流I减小,电压表的读数U=E-I(R1+r),I减小,其他量不变,则U增大,即

变大.通过电流表的电流I3=I-I2,I减小,I2增大,则I3减小,即有

变小.

故选B

阅读理解

书面表达。

                                       Does the bird know English?

     Dick's parents work in China. They couldn't leave the boy in Canada by himself and brought the

boy to Beijing four years ago . The boy began to study in a school last year and made friends with some

Chinese children . He's friendly to them and they like him . They often talk in Chinese and he often

teaches his friends some English .

     One Sunday Dick and his friends went to a forest to catch some birds . It was fine that day and they

saw a lot of flowers there . The children enjoyed themselves . Suddenly (突然) Dick saw a bird in a tree.

he wanted to tell him friends about it , but he was afraid it could hear him . He though for a while and

called out in English, "Look ! There's a bird in that short tree !"

     The bird heard him and flew away .

     "How clever your bird is! " said the boy . "It knows some English, too ! "

1. Dick began to study in Beijing because ______.

A. he was born in China.

B. he knows some Chinese

C. his parents work in China

D. he has some friends in China

2. His friends like Dick because ______.

A. he's friendly to them

B. he teaches them English

C. they can talk in Chinese

D. he often helps them

3. The children enjoyed themselves ______ that day.

A. at school

B. at home

C. in the park

D. in the forest

4. ______, so he told his friends in English .

A. Dick forgot to spell the word "bird" in Chinese.

B. Dick thought the bird only knew Chinese.

C. Dick hoped to frighten (吓唬) the bird away.

D. Dick wanted to catch the bird by himself.

5. Which of the following is right ?

A. The bird knew some English, too.  

B. Dick's cry frightened the bird away.

C. The Chinese bird was very clever.  

D. Dick wanted to help the bird fly away.

填空题