1.注意        2. 出发         3. 离开       

5. Many people were hurt       (在事故中) .

4. You should go out to play        (而不是) just studying indoors.

3. People have cut down too many trees.        (结果) ，the environment is getting worse and worse.

2.             (数以千计的) people came to the cities to work in the factories in the past.

1. Traffic        the roads        (使... 更拥挤) ，and it also makes pollution worse.

5. The animals are given food once a day. (对画线部分提问)

            are the animals given food?

4. More people drive cars. They don't ride bikes. (改为同义句)

 More people drive cars                    bikes.

3. Tom runs faster than any other student in his class. (改为同义句) 

Tom              in his class.

2. The box is so heavy that I can't carry it. (改为同义句) 

The box is        heavy        me        carry.