I ______ go to bed until my father ______ back. [ ]

He asked Tom, “Have you finished your homework？”－He asked Tom　　　　.

I think this is the most interesting thing _____ has happened to us .

Why does Mary look so sad? – Maybe the things _______ she saw made her think of her grandmother.

There are about more than five ___________ “left-behind” students (留守学生) in China.