Have you ever heard an echo of your voice?
An echo is a reflected(反射)sound. Stand in a very large, empty hall with nothing on the walls. Then shout. The sounds you make will hit the walls and come back to you. The walls reflect the sounds. These reflected sounds are called “echoes”.
We can use reflected sound to make sound travel farther. Hold a watch about fifty centimeters from your ear. You cannot hear it. The sound of the watch travels a short way in all directions. It does not travel as far as your ear. You can make it travel to your ear by using a roll of cardboard(纸板筒).
Make the roll of cardboard about fifty centimeters long. Put one end over your ear and hold the watch at the other. Now you can hear the watch because the sound has not gone in all directions. It is reflected down the roll to your ear.
A megaphone(喇叭筒)works in the same way. It makes sound travel farther. It reflects the sound into a beam which can travel a long way. In the ship, the sailor uses the megaphone to make his voice travel. Without the megaphone, his voice cannot travel far.
We use reflected sound in many ways. We use it to measure the depth of the sea, for example. Among the animals, bats and whales use reflected sound to tell them where they are and what things are near them.
1. Which is the right order of hearing our echo in a very large, empty hall?
a. We hear the reflected sound b. The sound returns to us
c. The sound hits the walls d. We make a sound
A.c, b, a, d |
B.c, a, b, d |
C.d, c, b, a |
D.d, b, c, a |
2.. From the text we learn that __________ .
A.reflected sound is useful only to blind people |
B.people haven’t made use of reflected sound yet |
C.bats use reflected sound to fly and get food |
D.whales don’t use reflected sound as they live in the sea |
3. If you haven’t got a megaphone, ____ will help you to make your voice travel farther.
A.a long piece of wood |
B.a roll of cardboard |
C.a thin thread |
D.a long piece of silk |
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根据短文内容及所给首字母提示写出所缺单词, 并将完整单词填在下面对应题号后的横线上。
Air is very important to everything that lives. But the air we breathe is g 1 dirty. People all over the world are looking for w 2 to make it clean again.
Have you e 3 watched the smoke from chimneys(烟囱) rising high in the air? Have you s 4 the smoke from cars and trucks on roads or the smoke from planes? The smoke is not g 5 to breathe. If we want to keep healthy and strong, we need to breathe c 6 air.
W 7 more and more factories everywhere and more and more cars, trucks and planes, it is getting harder and harder to do with the air p 8 .
Scientists have a 9 taken actions to stop or slow down some of the things that make the air dirty. They will not stop working u 10 we have clean air again.
1. 2. 3. 4. 5.
6. 7. 8. 9. 10.
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根据首字母 及上下文提示完成对话
A: Have you e_80___ been to Tokyo?
B: No, I have n___81__ been there before. But this summer I will go there with my parents.
A: I am s__82__ you will like it. My uncle u__83___ to work in Tokyo. But now he has g__84___to Paris for an i___85___ meeting. He will give a talk about how to p____86___ whales next week.
B: Paris? That is a really wonderful city with a very b__87_______ view.
A: R___88____? H__89___ I wish I could go there!
80____________81_____________82______________83______________84_____________
85____________86______________87_____________88______________89_____________
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