摘要:17.It’s sunny/rainy/snowy/windy .

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The air around the earth is called atmosphere. It’s up to more than 600 miles high. Airplanes fly only a few miles high in the air. The atmosphere makes the temperature on the earth so good that a great number of living things can stay alive. Air is all around us. Air is a mixture of gases(气体) that we can not see. About one fifth of the air is oxygen, which is needed by all living things. About four fifths of the air is nitrogen(氮). Plants need it to live. There are other gases in the air. The most important among them is carbon dioxide. Green plants use carbon dioxide to make food. People give off carbon dioxide when they breathe. Air has weight and takes up space. Air pressure (压力) inside our body is almost the same as air pressure outside. Because of this balance, we don’t feel the pressure of the air on us. Since the sun’s heat affects the earth’s air, the weather conditions on the earth change greatly: warm or hot; cool or cold; sunny or cloudy; windy, rainy, or snowy.When temperature changes, what happens to the air? When air is being heated, it expands(膨胀). That means it takes up more space. When air is being cooled, it takes up less space, or contracts(收缩).

(1)

We call the air around the earth ________.

(2)

About twenty percent of the air is _________.

(3)

When people breathe, they give off ________ used to make food by green plants.

(4)

Although air has ___________ , we don’t feel its pressure on us.

(5)

The weather on the earth is changeable because of ___________ .

(6)

When the air temperature gets higher, the air ___________ .

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Zhang Feng,in Beijing, is taking his vacation.He can't go out to play today because it is snowing outside.He is calling his pen pals and asking them what they are doing.

1.It's                              in Beijing.

A.windy                                 B.rainy                                    C.sunny                                     D.snowy

2.Why does Zhang Feng call his pen pals?

A.Because he is taking his vacation.

    B.Because he wants to know what his pen pals are doing.

    C.Because he wants to play with his pen pals in the snow.

    D.Because he likes talking with his pen pals on the phone.

3.What is Bob doing?

A.He is taking photos.                                                            B.He is skating.

    C.He is playing soccer.                                                                     D.He is watching.

4.Who is Dave relaxing with on the beach?

A.His friends.                                                                               B.His parents.

C.Bob.                                                                                                            D.His classmates.

5.Which of the following is TRUE according to the passage?

A.Dave and his friends are relaxing on a beach.

    B.A group of people are playing soccer in the heat.

    C.Bob and his friends are having a good fun in a park.

    D.Dave's parents are swimming at the pool.

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