The World War II made_________ impossible for Einstein to go on with his research.
The warmth of __ sweater will of course be determined by the sort of __ wool used.
Mr. Smith, there’s a man at __ front door who says he has __ news for you of great importance.
There are only twelve_____in the hospital.
Mr Smith has two______ , both of whom are teachers in a school.
——How many ______does a cow have? ——Four.