我国公元前2世纪就有人用冰透镜取火，这利用了凸透镜对太阳光的______作用．渔民可以利用电子发声器把鱼吸引到网里，表明______．
（1）让太阳光通过凸透镜，光线会聚焦点，从而使热量集中到焦点上．如果在焦点处放些易燃物质，易燃品就会燃烧起来，从而取火，正是利用了凸透镜的会聚作用．
（2）渔民可以利用电子发声器把鱼儿吸引到网里面来，表明水能够传播声音．
故答案为：会聚；水能够传播声音．
| 完形填空。 | |||
| In today's world many people seem to be hungry for money. Some of them even lost their lives for it. 1 does have its most useful effect on the poor. But if a person has a rich life, a lot more money doesn't mean 2 happiness. If money were everything, all 3 people would have true love, real friendship, health and long life. 4 , this is not always true. Nothing else is more pleasant 5 the three words "I love you". But can love be bought? I'm afraid not. Love means "give", not "take". 6 and a long life are probably the most expensive things for every 7 . Well, can health and a long life be bought with money? The answer is "No". Of all the people 8 live longest in the world, few of them are millionaires. Real friendship can't be bought , either. In a word, where money is worshiped, money can make 9 argue , lovers hate , and strangers fight with each other and so on. No matter 10 money you have, it is still not enough to make you a happy person if you have no one to laugh with and no one to cry for. | |||
| ( )1. A. Money ( )2. A. some ( )3. A. poor ( )4. A. But ( )5. A. to ( )6. A. Health ( )7. A. child ( )8. A. what ( )9. A. teachers ( )10. A. how many | B. Love B. many B. happy B. Then B. than B. Healthy B. man B. which B. birds B. how much | C. Time C. more C. lucky C. However C. from C. Happy C. person C. who C. brothers C. how often | D. Friendship D. a little D. rich D. So D. with D. Happiness D. woman D. whom D. students D. how long |