问题 填空题

雷电是常见的自然现象,雷电发生时常常先看见闪电后听到雷声,这是因为______.

答案

因为在我们生活的环境下,光的传播速度远远大于声音的传播速度,所以在雷电发生后,从同一点出发的雷声和闪电,会是闪电先到而雷声后到.

故答案为:光速大于声速

阅读理解

阅读理解。

     How many kinds of shapes (形状) can you name? If something is round, what do you call it? You call it

a circle. What can you see around you that looks like a circle?

     Another shape is square. A square has four sides. Each side is the same length (长度). A square has four

corners called right angles (直角).

     A triangle is also a shape. The prefix "tri" on the base word "angle" means "three". A triangle always has

three sides and three angles.

     All the pages of your textbooks have four square corners, but the pages are not square. Can you tell why

not? It is because the sides of each page are longer than the ends. Shapes like this are rectangles. You can say

that they are rectangular shapes.

      If you are given a piece of paper which is a rectangular shape, can you make the paper into a square? The

answer is "Yes", and it seems not so difficult. Now fold the square. What shape have you got? Do you think

it's very interesting?

1. You usually learn the knowledge discussed in this passage in _____ classes.

A. chemistry

B. math

C. history

2. Picture _____ is a rectangle.

A.  B.  C.

3. Picture _____ shows the right marks of"side & end" according to the passage.

A.  B.  C.

4. Fold a square in the way of the picture shown on the right, you may get a shape of _____.

A. square

B. rectangle                                       

C. triangle

5. In this passage, we've learned about _____ kinds of shapes.

A. three

B. four

C. five

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