–Look at that girl! Is it Susan? --No, it _______ be her. She went to her hometown just now.
It used to be very quiet and ______ ever happened around here.
He hurried back home _________ his schoolbag.
When he saw a wallet on the ground, he ________at once.
The train was late, ______ we had to wait for half an hour.
After a long walk, the old man ___________be tired now.