_______have you been learning to swim?—Half a year. [ ]
I don’t know if he __________ tomorrow . If he _______ here , I will call you .
It is impossible for____________ little room.
The man in a black suit _______ be our youth worker. — I’m sure it _____ be him. I saw him in the laboratory building some minutes ago.
If _____ carefully, the experiment will be successful.
