对以下物理现象的正确分析是
①从射来的阳光中，可以看到空气中的微粒在上下飞舞
②上升的水蒸气的运动
③用显微镜观察悬浮在水中的小炭粒，小炭粒不停地做无规则运动
④向一杯清水中滴入几滴红墨水，红墨水向周围运动
A．①②③属于布朗运动
B．只有④属于布朗运动
C．只有③属于布朗运动
D．以上说法均不对
答案：C
布朗运动是悬浮在液体里的固体小颗粒的无规则运动，C对；①中的微粒运动没有固定轨迹，是由于风力的作用②是由于压强的作用④是扩散现象
| 完形填空。 |
| It is a thousand kilometers across that desert (沙漠). The road is 1 nearly all the way. Sometimes there is a deep sand. A driver must then put his foot down hard and drive through! There are three small 2 along the way. Vick reached the first place at ten o'clock p. m. He had his 3 in a little restaurant (餐馆) there. It was a warm 4 in August. Vick wanted to 5 through the night. The nights are warm enough in August, but the days are very, very 6 . He left the restaurant at 11: 30 and drove over 7 hours. There wasn't a moon, but the 8 were wonderful. There was nothing else on die road. Vick thought, "It's an empty desert. No tree, house, man. "He could 9 . the endless, white road in the car's headlights (车灯). A million stars looked down on him. It was two o'clock in the morning. Vick stopped the car. He was two hundred kilometers from the 10 town: "I'll light the cooker (炊具)," he thought, "and make some tea. " He got out of the car. He heard some sounds, ten or fifteen metres 11 . He could not see anything in the darkness (黑暗). A man said, "Good morning. It's a 12 morning, isn't it?" The man came forward (向前), out of the darkness; out of the desert. Vick did not move. The man said, "You are going to 13 some tea, aren't you? I often get a cup of tea at this time. It" s two o'clock. Cars always 14 near here at this time. Sometimes I get a 15 . Now listen, and I'll tell you a story. Then you'll give me..." |
| ( )1. A. short ( )2. A. cities ( )3. A. tea ( )4. A. night ( )5. A. live ( )6. A. cold ( )7. A. two ( )8. A. trees ( )9. A. see ( )10. A. home ( )11. A. about ( )12. A. noisy ( ) 13. A. eat ( )14. A. leave ( )15. A. bread | B. good B. hotels B. supper B. day B. stay B. cool B. seven B. animals B. ride B. other B. from B. lovely B. make B. stop B. car | C. busy C. villages C. lunch C. season C. drive C. hot C. ten C. stars C. pass C. next C. far C. sleepy C. cook C. meet C. rest | D. well D. towns D. breakfast D. month D. walk D. warm D. fourteen D. clouds D. find D. last D. away D. sunny D. drink D. run D. meal |
