---Which book do you think is the most useful to my studies?---________, as long as you read it. In fact, they are out of date.

I hope there are enough glasses for each guest to have____ . 

One should wash ___ hands before meals.

For many seniors in some universities, the final year can be an unpleasant experience, _______ that ends the campus romance.

 I'm moving to the countryside because the air there is much fresher than _______ in the city.