It is essential that these application()forms back as early as possible.

单项选择题Someone is knocking at the door. It () my mother. It's time for her to be back.

A．can he
B．may not he
C．must be
D．mustn't be

单项选择题Nobody but Jane () the secret.

A．know
B．knows
C．have known
D．is known

单项选择题My postcard is still on the desk. Why () you () it

A．haven't; posted
B．didn't; post
C．wasn't; posting
D．won't; post