问题 选择题

下列现象中属于凝华现象的是  (      )

A.冬天的早晨树木上挂满了霜

B.秋天的早晨花草叶子上的露水

C.在教室里洒水后地面变干

D.早晨的浓雾

答案

答案:A

题目分析:A、霜是空气中的水蒸气遇冷凝华为固体的冰晶,附着在建筑物或植被表面;故A正确;B、露是空气中的水蒸气遇冷液化为液态的小水滴,附着在植被表面;故B错误;

C、洒在地上的水变干,是水发生了汽化(蒸发)现象,形成了水蒸气散发在空气中;故C错误;D、雾是空气中的水蒸气遇冷液化为液态的小水滴;故D错误;故选D.

点评:在一定条件下,物体的三种状态--固态、液态、气态之间会发生相互转化,这就是物态变化;物质由气态直接变为固态叫凝华,物质由固态直接变为气态叫升华;由气态变为液态叫液化,由液态变为气态叫汽化;由固态变为液态叫熔化,由液态变为固态叫凝固。

阅读理解

The best way of learning a language is using it. The best way of learning English is talking in English as much as possible. Sometimes you'll get your words mixed up (混合) and people will not understand you. Sometimes people will say things too quickly and you can't understand them. But if you keep your sense of humor, you can always have a good laugh at the mistakes you make. Don't be unhappy if people seem to be laughing at your mistakes. It's better for people to laugh at your mistakes than to be angry with you, because they don't understand what you are saying. The most important thing for learning English is: "Don't be afraid of making mistakes because everyone makes mistakes."

1. The writer thinks that the most important thing for you to learn a language is___________.

A. reading      B. writing     C. using     D. listening

2. What should you do in learning English?

A. Try to make some mistakes.              B. Avoid making any mistakes.

C. Remember as many new words as you can.  D. Use it as often as you can

3. If people laugh at the mistakes you make, you should ___________.

A. be angry with them                 B. be angry with yourself

C. not care                          D. believe you are right

4. When you make a mistake, you should___________.

A. never make any mistakes again     B. tell others not to make the same mistake

C. punish yourself for making it       D. keep your sense of humor

5. The story tells us:" ___________."

A. It is normal (正常的) that we make some mistakes in learning English

B. Everyone must make mistakes

C. We can avoid making mistakes in learning a language

D. Laughing can help one learn English well

单项选择题