1 . -It ________Jack who is at the gate of the library.
-It ________him. I saw him off at the railway station just an hour ago.

A．can be; can't be	B．must be; can't be
C．can be; must have been	D．must be; can't have been

2 . He______ his work, otherwise, he wouldn’t be enjoying himself by the seaside.

A．must have completed	B．should have completed
C．ought to complete	D．must complete

3 . Helen________ go on the trip with us, but she isn’t quite sure yet.

A．shall

B．may

C．must

D．can