问题 填空题

如果一个振动的物体发出了声音,而我们却听不到这个声音,可能的情况是______和______.

答案

听到声音需要两个条件:一是物体振动频率在20Hz~20000Hz;二是需要有声音传播的介质;二者缺一不可;

故答案为:低于听觉频率范围20Hz~20000Hz;在声源和人耳之间没有传播声音的介质.

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How many things can you see in the night sky? A lot! On a clear night you can see the moon, some planets, and thousands of sparking stars.

You can see even more with a telescope. You might see that many stars look larger than others. You might see that some stars that look white are really red or blue. With bigger and bigger telescopes you can see more and more objects in the sky. And you can see those objects in more and more detail.

But scientists believe there are some things in the sky that we will never see. We won’t see them with the biggest telescope in the world, on the clearest night of the year.That’s because they’re invisible. They’re the mysterious dead stars called black holes.

You might find it hard to imagine that stars die. After all, our sun is a star. Year after year we see it up in the sky, burning brightly and giving us heat and light. The Sun certainly doesn’t seem to be getting old or weak. But stars do burn out and die after billions of years.

As a star’s gases burn, they give off light and heat. But when the gases run out, the star stops burning and begins to die.

So next time you look up at the night sky, remember: there’s more in the sky than we can see!

小题1:On a clear night we might see things except______.

A.the moon

B.some planets

C.sparkling stars

D.the sun小题2:How can we see even more in the sky?

A.By using a telescope

B.By using a microscope

C.By climbing up to the top of a mountain

D.By going outside on a clear night.小题3:What does the underlined word”invisible”mean in Chinese?

A.看不见的

B.听不见的

C.摸不着的

D.无形的小题4:When a star’s gases_______,the star begins to die.

A.burn

B.run out

C.give off heat

D.get weak小题5:Which of the following is NOT TRUE according to the passage?

A.We might see that many stars look larger than others with a telescope

B.We might see that some stars that look white are really red and blue with a telescope.

C.We can see some objects in more and more detail with bigger and bigger telescopes.

D.The sun certainly seems to be getting old and weak.