—How many times have you been to China? —In fact, it is the first time I __________ here.
__________ the students who have taken part in the sports game is unknown.
_______, the more exercise you do, the richer your knowledge will be.
His mother happened _______ when his program was shown on Channel Young.
By the time he was ten, Edison _________ experiments in chemistry.
The businessperson wanted to sell his goods fast; ______, he chose his partner with great care.