目录 1
Unit 13 Merry Christmas! 1
Unit 14 Mainly revision 11
Unit 15 At home with the twins 21
Unit 16 What s it made of? 29
Unit 17 What was it used for? 40
Unit 18 Planting trees 54
Unit 19 Mainly revision 68
Unit 20 The world s population 76
Unit 21 Shopping 84
Unit 22 At the doctor s 95
Unit 23 The football match 104
Unit 24 Mainly revision 114