问题 填空题

如图是利用放射线自动控制铝板厚度的装置的示意图.生产线压制的是2mm厚的铝板,放射源能放射出α、β、γ三种射线,铝板下的探测接收器可以把接收到的放射线的强度转化为电信号,通过微机控制轧辊间的距离从而控制铝板的厚度.根据α、β、γ三种射线贯穿性能的不同,可以判定三种射线中______射线一定能穿过这样的铝板,______射线对控制铝板厚度起着主要作用.

答案

α、β、γ三种射线的穿透能力不同,α射线不能穿过3 mm厚的铝板,γ射线又很容易穿过3 mm厚的铝板,厚度的微小变化不会使穿过铝板的γ射线的强度发生较明显变化,所以基本不受铝板厚度的影响.而β射线刚好能穿透几毫米厚的铝板,因此厚度的微小变化会使穿过铝板的β射线的强度发生较明显变化,即是β射线对控制厚度起主要作用,所以可以判定三种射线中γ  射线一定能穿过这样的铝板,β射线对控制铝板厚度起着主要作用.

故答案为:γ    β

阅读理解

阅读理解。

     It was Sunday and the weather was fine, so Mrs. Black said, "Let's go for a picnic (野餐) . " "Oh, yes!" said Mary

and John, her two children. Mr. Black said, "Yes, let's go to the woods (小树林) and have our picnic there. " "Good.

Help me to get the things ready. " "All right, said the children. John brought the basket for the food and the bottles

for the water. Mary brought a blanket (毯子), while Mother made the sandwiches, and Father put water and oil into

the car.   Soon everything was ready and they left the house. When they got there,   Mary put the blanket on the

ground. John took the food out of the car, Father made a fire and Mother made tea. "Isn't it beautiful here?" said

Mother. "It's very quiet and green." John had a kite and soon he was running with it. "Be careful!" shouted Mother,

but it was too late. John fell(摔倒) over basket of food, and everything fell out. "Look!" cried Mary.  "There are ants

(蚂蚁) in the food. Yes, there were. " There were hundreds of them. The blanket was on an ants' nest.  (蚂蚁窝)

1. How many people were there in the story  

A. 3      

B.  4      

C.  5      

D.  6

2. When did the Blacks go for a picnic?

A. Last Sunday

B. On Monday

C. On Tuesday  

D. On Wednesday

3. What did they prepare (准备) for the picnic?

A. basket, water, oil, sandwiches and bottles  

B. bottle, basket, oil, and blanket

C. basket, water, oil, blanket and sandwiches  

D. sandwiches, blanket, water and basket

4. Who made a fire?  

A. Father  

B. Mother  

C. John    

D. Mary

5. Did they have a good picnic?  

A. Yes, they did  

B. Yes, they do    

C. No, they don't

D. No, they didn't  

单项选择题