—What’s up? You look down. —I have piles of papers ________, but I type so slowly.
No sooner ________ stepped on the stage than the audience broke into thunderous applause.
The yellow house ________ windows face south is the place ________ I spent my childhood.
Because Sarah has always saved __________, she is now able to afford a big house.
--Reading is the best way to pass time on the train. --, I never go traveling without a book.
When it ________ air pollution, Beijing faces the three “C”s, cars, coals and construction, which lead to Beijing’s thick air pollution.