—Where have you been, David? You're late for class again.—________ My bus got caught in a traffic jam.
_____________ cease(终止) advertising, prices would be significantly reduced.
Much labor would have been saved if the electronic computers_____________ before.
There was a(n)________silence in the live interview,when no one knew what to say to the audience.
Doctors are doing research to find out what happens physically when people______ smoking.
Once you get _______ something, it is very hard to ________.