【題目】Scientists have advanced many theories about why human beings cry tears, none of _________ has been proved.

【題目】When their children lived far away from them, these old people felt _________from the world.

【題目】A sudden stop can be a very frightening experience, _________ if you are travelling at high speed.

【題目】Every student as well as some teachers who_____ to visit the museum _____ required to be at the bus station at 6:30.

【題目】The study suggests that the cultures we grow up _________influence the basic processes by which we see world around us.

【題目】To return to the problem of water pollution, I’d like you to look at a study _________ in

【題目】——Shall I tell John about it?

【題目】George _________ too far. His coffee is still warm.