1 . Black holes________not be seen directly so determining the number of them is a tough task.

A．can

B．should

C．must

D．need

2 . People liked O. Henry’s stories, because simple as the tales were, they ______ finish with a sudden change at the end, to the readers’ surprise.

A．could

B．would

C．might

D．must

3 . They________ every means, but the engine ________work.

A．tried; couldn’t	B．have tried; won’t
C．tried; won’t	D．have tried; can’t

4 . I advise you to stay away from Mary. Although she is usually easy-going, she ______be quite annoying sometimes.

A．can

B．need

C．must

D．should

5 . —The test is very important to us. Do you think so?
—Yes, so we ________ be too careful during the test.

A．mustn’t

B．daren’t

C．needn’t

D．can’t

6 . Social media platforms make different voices heard, but they ______ also spread false information.

A．must

B．can

C．should

D．need

7 . This road is narrow and the traffic on it is heavy, so sometimes it ______ be blocked.

A．should

B．shall

C．can

D．need

8 . My nephew William is still a puzzle to me—sometimes he is as quiet as a mouse, while he______be fairly active at other times.

A．should

B．need

C．must

D．can

9 . Generally speaking, it’s very hot in summer in my hometown, but at times it ______ be cool.

A．need

B．must

C．can

D．should

10 . —— Look at the man in pink over there! Is he John?
—— He ________ be John who is away on a business trip now.

A．shouldn’t

B．mustn’t

C．may not

D．can not