Another drug that has helped improve people’s health is penicillin, _________ is _________ by many _________ one of the most important medicines.

Do you know_____ ? Sorry,I’ve no idea.

“Did you have any difficulty in yesterday’s homework?”—“No, in fact I found _____.”

Look at that girl! Is it Susan?—No, it _______ be her. She has gone back to her hometown.

It takes Jill 10 minutes________ to school every morning.