Unit 1 The Changing World 1
1．My hometown has become more and more beautiful 1
2．China has the largest population 9
3．The world has changed for the better 17
Unit 2 Saving the Earth 25
1．Pollution causes too many problems 25
2．All these problems are very serious 33
3．Would you like to be a greener person? 41
Review 1 49
Unit 3 English Throughout the World 53
1．English is used more and more widely around the world 53
2．English is spoken differently in different countries 61
3．Could you give us some advice on how to learn English well? 69
Unit 4 Amazing Science 77
1．Spaceships are mainly controlled by computers 77
2．When was it invented? 85
3．I don't think aliens can be found in space 93
Review 2 101