Loulan, once a small, wealthy commercial city, is believed by many people___________over gradually by sandstorms from AD 200 to AD 500.
Sally had no pen ____ yesterday morning.
--Hi, Betty. Shall we go swimming this Sunday? --This Sunday? I am sorry, I have a lot of homework ____ this Sunday.
Although Jeff loves KFC, he tries ____ it too often.
Who do you think you’d like ____?
When you leave, don’t forget ____ off the light.