____ students are there in your class?— Forty-one. [ ]

In the future people can read books only _____ computers, not _____ paper.[ ]

Bob,_______ your coat. It’s cold and windy outside.

I hear Sam has gone to Qingdao for a holiday.—Oh, how nice! Do you know when he________?

It will _______ hundreds of years to make robots think like a human.