Tom ____ be ill, for I saw him playing basketball an hour ago. 

You'd better take a heavy coat. Sometimes it ______ be very cold.

--- ______ you give your seat to this old man? --- Of course. 

No student ______ go out of school for snacks during the break without the teacher’s permission.

If you ___ stick to the unrealistic approach, the worse result will be waiting for you not far ahead.