You didn't take his advice. ________ his advice, you ________ such a mistake.
—Must I turn off the gas after cooking ? —Of course . You can never be _______ careful withthat.
_____ is known to everybody, the moon travels round the earth once every month.
It is so difficult a problem that _____ student in this class _____ work it out.
Shirley _____ a book about China last year, but I don't know whether she has finished it.
Who did the teacher have ___ an article for the wall newspaper just now?