Many more policeman should be sent to ________them ________some endangered animals.

We can’t wait. We have to_________ the direction and the distance before we take action.

Last summer I took a course on _______ poisonous gases

There is a discount for the cost of the 6-week English course _____ you pay in advance.

It is the first time that we ________ a film in thecinema together as a family．