They __________ two free tickets to Canada, otherwise they’d never have been able to afford to go. 

 The hotel wasn't particularly good，but I ________ in many worse hotels.

The old professor has such a bad memory that he looks for the watch while he is ___.

The first use of atomic weapons was in 1945, and their power ________ increased enormously ever since. 

He is a kind-hearted boy and he will come to the Old Folks' Home whenever __________.