I ___________ through that bitter period without your generous help.

Without gravity, we _____ walk on the ground as freely as we do now. 

--Listen! Tom is singing in the next room.--It _______ be Tom. He has gone to Shanghai. 

According to the rules and regulations, all payments _____ be made in cash in the shopping center.

“Mike is often absent from class.” “Tell him he _     _ answer for it if he goes on behaving like that.”