问题 单项选择题

关于电容充放电式X线机的描述,正确的是

A.对供电电源要求很高
B.X线管阴阳两极只要一加高压就产生X线
C.三极X线管
D.控制灯丝电压来控制X线的发生与停止
E.曝光时有较明显的电源电压下降

答案

参考答案:C

解析:由于使用的三极X线管栅极控制存在负电位,X线不能发生。

阅读理解

阅读理解

     The White family come to a new big city, but Mrs White's son, Bob, is not happy. He doesn't

have anyone to play with. "Don't worry!" says his mother. "You will soon make friends here."

     One morning, there is a knock at the door. Bob's mother, Mrs White, opens it. There stands

a woman with brown hair. It is Mrs Miller. She comes to borrow two eggs. She wants to make

cakes. Mrs White gives her two. In the afternoon there is another knock at the door. Mrs White

opens it and she sees a boy standing there. "My name is Jack Miller," he says. "My mother sends

you this cake and the two eggs."

     "Well, thank you , Jack," says Mrs White. "Come in and meet my son Bob."

     Look! Bob and Jack are having cake and milk. They are playing football. Now they are friends!

Jack says, "I'm glad you live next door." Bob says, "I must thank your mother for coming to borrow

eggs." Jack laughs and tells Bob, "My mother doesn't want the two eggs, but she wants to make

friends with your mother. " Bob says, "That's a funny way to make friends. It's an easy way, too.

It can work!

1. Bob feels __________ when his family moves to a new city.

A. unhappy

B. happy

C. tired

D. busy

2. Mrs Miller __________ one morning.

A. gives Mrs White a piece of cake

B. asks Bob to play with his son

C. borrows eggs from Mrs White

D. lends two eggs to Mrs White

3. In the afternoon __________ have cake and milk together.

A. Jack and Mrs Miller

B. Bob and his mother

C. Mrs White and Mrs. Miller

D. Bob and Jack

4. Which of the following is true?

A. Mrs Miller is Mrs White's old neighbor(邻居).

B. Mrs Miller wants to make friends with the Whites.

C. There aren't any eggs in Mrs White's home one morning.

D. There aren't any eggs in Mrs Miller's home.

5. The best title of this passage is __________.

A. Way to Borrow Eggs

B. Way to Make Cakes

C. Way to Make Friends

D. How to Make Cakes

配伍题 B型题