Tom was walking along the riverside when he heard someone calling him from behind. He turned around_______ found nothing.
There _____ an exciting party at Mr. Wang’s this evening.
Are you free now? I have ___________ to tell you.
There is a ______ tree in our school.
He spent a week ____ the novel.
— I broke the window. — You ____ play football near the window. A should B. shouldn’t C. had better D. must