How did the thief come into the house?—He came into the house _____ the back door.[ ]

Where has your father gone? He has gone to Shanghai.And he’ll ______for three days.

The old scientist devoted most of his time ___________ the space science.

We know Jackie Chan _____ movies are very popular with the young. [ ]

Sun Tao has had a_______ English course, but he still doesn’t know