4.We ____ have proved great adventures, but we have done the greatest march ever made in the past ten years. A. needn’t B. may not C. shouldn’t D. mustn’t 5. Black holes ____ not be seen directly, so determining the number of them is a tough task. A. can B. should C. must D. need 6. --I think I’ll give Bob a ring . --You ____.You haven’t been in touch with him for ages A. will B. may C. have to D. should

B

A

D