1 . —-Who’s the man over there? Is it Mr. Black?
—It______be him. He’s much taller.

A．may not

B．can’t

C．will not

D．mustn’t

2 . So far no life has been found outside the earth, but while some scientists are actively searching for living things in outer space, others firmly believe there ____ .

A．mustn’t be

B．may not be

C．can’t be

D．won’t be

3 . Remember to pack more winter clothes into your suitcase. The winter in Chicago __________ be extremely cold.

A．must

B．will

C．can

D．shall

4 . Despite the fact that Lucy is a lovely girl, she _____ be extremely difficult to work with sometimes.

A．must

B．should

C．would

D．can