She often thinks that he will succeed if he works hard, _____?[ ]

A. doesn't she  

B. won't he

C. isn't she  

D. doesn't he

The number of workers in this factory _____ 1,500.

A number of them _____ from the countryside. 　　[ ]

A. is; are

B. are; is

C. is; is

D. are; are