David is often absent from class.—Tell him he ________ answer for it if he goes on behaving like that.

I haven’t seen your father for days. Where is he—He Hong Kong on business for three days.

An awful accident __________, however, occur the other day.

Surely it doesn’tmatter where the student associations get their money from; what _______ iswhat they do with it

________ these experiments were successfully completed would we think of going into humans.