willit take us to fly to Hainan and willthe trip to Hainan cost us

The students usually need ________ sleep a night.

下列对加点的实词解释不正确的一项是（3分）

Excuse me, does Mr. Smith’s son live here—He _________ be here, but he has moved.

This question is so hard that very ______ students cananswer it.