1 . 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

2 . I guess this book ______ be Mary’s, but I’m not sure.

A．must

B．mustn’t

C．may

D．can

3 . — Will you be free this weekend?
— I’m not sure, but I ________ go to an art exhibition with my parents.

A．will

B．should

C．must

D．may

4 . — He is a very good tennis player; you __________ see him in action.
— Thanks for your advice.

A．are able to

B．ought to

C．mustn't

D．might not