问题 选择题

雷达是用来对目标进行定位的现代化定位系统,海豚也具有完善的声呐系统,它能在黑暗中准确而快速地捕捉食物,避开敌害,性能远远优于现代化的无线电系统.

(1)海豚生活在(    )

A.沙漠             B.陆地             C.树上             D.海中

(2)海豚的定位是利用了自身发射的(    )

A.电磁波           B.红外线           C.次声波           D.超声波

(3)雷达的定位是利用自身发射的(    )

A.电磁波           B.红外线           C.次声波           D.光线

答案

(1)D (2)D (3)A

(1)海豚生活在海中,选D.

(2)海豚能发射超声波,那是一种频率高于2×104 Hz的声波,它的波长非常短,因而能定向发射,而且在水中传播时因能量损失小,要比无线电波和光波传得远,海豚就是靠自身发出的超声波的回声在混浊的水里准确确定远处的小鱼位置而猛冲过去吞食,选D.

(3)雷达是一个电磁波的发射和接收系统,因而是靠发射电磁波来定位的,选A.

单项选择题
单项选择题

Children start out as natural scientists, eager to look into the world around them. Helping them enjoy science can be easy ;there’s no need for a lot of scientific terms or expensive lab equipment. You only have to share your children’s curiosity. Firstly,listen to their questions. I once visited a classroom of seven-year-olds to talk about science as a job. The children asked me" textbook questions" about schooling, salary and whether I liked my job. When I finished answering, we sat facing one another in silence. Finally I said, "Now that we’ve finished with your lists, do you have questions of your own about science"
After a long pause ,a boy raised his hand," Have you ever seen a grasshopper(蚱蜢) eat When I try eating leaves like that, I get a stomachache. Why"
This began a set of questions that lasted nearly two hours.
Secondly, give them time to think. Studies over the past 30 years have shown that, after asking a question, adults typically wait only one second or less tor an answer, no time for a child to think. When adults increase their" wait time" to three seconds or more, children give more logical, complete and creative answers.
Thirdly, watch your language. Once you have a child involved in a science discussion, don’t jump in with" That’s right" or" Very good". These words work well when it comes to encouraging good behavior. But in talking about science, quick praise can signal that discussion is over. Instead, keep things going by saying" That’s interesting" or" I’d never thought of it that way- before", or coming up with more questions or ideas.
Never push a child to" Think". It doesn’t make sense, children are always thinking, without your telling them to. What’s more, this can turn a conversation into a performance. The child will try to find the answer you want, in as few words as possible, so that he will be a smaller target for your disagreement.
Lastly, show;don’t tell. Real-life impressions of nature are far more impressive than any lesson children can learn from a book or a television program. Let children look at their fingertips through a magnifying glass, and they’ll understand why you want them to wash before dinner. Rather than saying that water evaporates, set a pot of water to boil and let them watch the water level drop.

According to the passage, children can answer questions in a more logical, complete and creative way if adults______.

A. ask them to answer quickly
B. wait for one or two seconds after a question
C. tell them to answer the next day
D. wait at least for three seconds after a question