—Excuse me, could you help me take this chair to my office?—I’m sorry, ______ I can’t help you right now. I’m too busy.
Do you know _________ an “o” and _________ “u” in the word “computer”?
The Yangzhi River is one of __________ in the world.
—How can we protect ourselves ________ the earthquake?—We should stay calm first.
Da Shan is _________ at Chinese. He can speak Chinese very _________.
—My mother has been ill for several days.—____________