---Look at the boy running on the playground. Is it David? ---It ______ be him. I saw him go to the teachers’ office just now.
It’s difficult _____ your sound because the noise is too high.
We don’t know If it _____. If it_____, we won’t go out for a walk.
The teacher is ____ with what we did.
Xi’an is very famous ______Terra Cotta Warriors (兵马俑).
Neither you or he ______ Hawaii before.