When it ________ air pollution, Beijing faces the three “C”s, cars, coals and construction, which lead to Beijing’s thick air pollution.
To fetch water before breakfast seemed to me a rule ________.
The patient was warned ________ oily food after the operation.
—What's the matter with Della?—Well,her parents wouldn't allow her to go to the party,but she still ________.
—Would you like to join me for a quick lunch before class?—________,but I promised Nancy to go out with her.
In my opinion,life in the twenty-first century is much easier than ________.