Not until World War II ______ to use new chemical techniques to purify penicillin.
The dying old man opened his mouth as if ____ something.
— Are you a teacher?— No, but I ____. I worked in a middle school for three years.
I wonder why you won’t do it as ____. It’s the third time you have done so.
— How are you getting on with your work?— Oh, I’m sorry. Things aren’t going so well as ____.
— Why do you want the book so much?— ____, sir.