—What time do we have to be at the gate of the museum?  —______ the visitors begin to check in.

The charity sale our school organizes every year has taught us much. _______ we would never have learned it in class.

It is _____ colder than yesterday; put on more clothes or you will catch a cold. 

There was a long queue for coffee. Having waited for 10 minutes, we _______ gave up.

The teacher told Tom to sit ______ in class.