Exercise 1 1
Exercise 2 5
Exercise 3 9
Exercise 4 14
Exercise 5（Test one） 18
Exercise 6 23
Exercise 7 27
Exercise 8 31
Exercise 9（Test Two） 36
Exercise 10 41
Exercise 11 45
Exercise 12 49
Exercise 13 53
Exercise 14 Test Three） 57
Exercise 15 62
Exercise 16 66
Exercise 17（Test Four） 70
Revision（Test Five） 75
Useful Expressions 88