are the Winter Olympic Games held—Every four years.

Was it in 2013, when he was still at a middle school, ________ this boy became an expert at the computer

_____ in the new on-line game , he missed the final boarding call of his flight .

____many times, he finally understood it.

I’m sorry, Mr. Li. I ________ my exercise book at home.—Oh, don’t forget ________ it here tomorrow, please.