问题 选择题

三个灯泡连接如右图所示,且电路电压U保持一定,原来电键S断开,则接通电键S时(   )

A.亮度不变,亮度增加

B.亮度增加,亮度减弱

C.亮度减弱,亮度增大

D.的亮度都增加

答案

答案:C

当开关闭合时,L3连入电路跟L1并联,使得总电阻减小,干路电路增大,故L2灯变亮,由于电源电压不变,所以L1两端电压减小,故L1灯变暗

所以应该选C

阅读理解

阅读理解。

     From the time we were babies we have been taught manners. We are taught how to hold a knife and

fork and not to talk with our mouths full. We are taught how to shake hands and when to stand and when

to sit and the way to introduce people.

     Sometimes good manners in one place are very bad manners somewhere else. Almost everywhere

eating together means that people are very friendly to each other. But in parts of Polynesia(波利尼西亚)

it is bad manners to be seen eating beside each other. So they politely turn their backs to each other when

they are taking food.

      Some East Africans spit four times as a kind of blessing(祝福). They do it to show that they want a

sick person to get well or to bless a newborn baby. In most other places, spitting means something

completely different. It usually shows an unhealthy habit. In many countries, it may mean that you hate

someone.

     When we go to visit someone we say "Hello!"Or"How are you?" or things like that. But if you are

visiting an East African village, everyone will be very careful not to pay attention to you. The polite thing

there will be for you to go quietly, without speaking to anyone, and sit beside your friend. You should

wait until he has finished what he is doing and then he will begin talking to you.

     In a village in Arab, a visitor will walk behind all the tents until he gets to the one he wants to visit. If

he passes in front, he will be invited into each tent and asked to eat. It is rude to refuse.

1. From this passage we know ______. 

A. it's good manners to use a knife and fork to eat

B. it's bad manners to stand and talk

C. it's good manners not to talk with our mouths full

D. how to shake hands when we introduce people

2. In many places, spitting may mean______.

A. you give a new-born baby the blessing

B. you want a sick person to get well

C. you hate someone

D. you show your love to your relatives or friends

3. If you visit an East African village, you ______.

A. should say"Hello!"or"How are you?"to others

B. should talk to the villagers quietly

C. should be very careful and not to pay any attention to others

D. must wait until your friend has finished his work and then begin to talk to him

4. Which of the following is right?

A. Spitting four times is a way of blessing for some East Africans.

B. You should talk to an East African as soon as you see him or her.

C. Eating together is always a symbol of friendship.

D. You are supposed to turn your back to others when you are eating in China.

5. If you are visiting a village in Arab, ______.

A. you will walk all the tents until you get to the one you want to visit

B. the host will offer you meals whenever you come

C. you'd better carry a tent with you

D. you are supposed to offer a helping hand in repairing the villagers' tents

单项选择题 A型题