--What about the protection? ---Let’s keep the surface ____ dirty by putting a cover over it.

 Mr. Smith went to a bookstore, where a lot of books were        .

Playing QQ’s “Happy Farm” by planting, watering, fertilizing, spraying, harvesting and selling of virtual vegetables, fruits and flowers, we can find out ________ all the excitement is about.

Nobody would stand out admitting the fact, for some reason,      they lost the game.

 I don’t think _____ possible to master a foreign language without much memory work.