What action should they _______ such a thing happening again?
_____ the Great Green Wall, the land produces (生产出) more crops.
—Where are Maria and Kangkang?—They _____ England.
—Do you know ______ ?—Sorry. I don't have a watch.
Mother is the person ______ is always there for you.
—Hey, Molly. You ______ on the phone just now.—Oh, I was in the library.