— How many left-behind children are there in your class? — .
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.—____________