Unit 15 At home with the twins 1
Unit 16 What's it made of? 14
Unit 17 What was it used for? 23
Unit 18 Planting trees 32
Unit 19 Mainly revision 40
Unit 20 The world's population 48
Unit 21 Shopping 57
Unit 22 At the doctor's 67
Unit 23 The football match 77
Unit 24 Mainly revision 86
期中检测题 92
期末检测题 103
附：练习参考答案 113