216. If you feel dizzy in a coal-burning room, that’s lack of . Please open the window and air the room at once.
__________ these tips, and your time _______ doing research on the Internet _________ much worthwhile.
While doubts about the medicine’s safety have____________, interest continues to grow.
Do you know in what circumstances was it____________ Jack achieved his goal?
If penicillin _____________ available, many people ______________ from sickness.
Another drug that has helped improve people’s health is penicillin, _________ is _________ by many _________ one of the most important medicines.