During the past three years, several earthquakes _______ in different places of the world.
A：happen
B：happened
C：took place
D：take place
一凡文具店每天上午8时开始营业，下午7时停止营业，每天营业____时。
一项工程，8人去做24天完成，现在要16天完成，每天应____人去做.增加____人．
