-----Each of the students in No.1 Middle School hard at his or her lessons, to go to university some day. ------So do I .
________ you happen to see Mary, would you please ask her to come here?
Everyone knows that _______ is dangerous to play with fire, but _______ is difficult is to prevent children from playing with fire.
Not until the early years of the 19th century ________ what heat was.
Tom kept quiet about the accident ________ lose his job.
A driver should __ the road when .