________, he can succeed in his work if he works hard.
Mr. Smith was so angry at all ______ Bill was doing ______ he left.
The traditional view is ______ we sleep because our brain is “programmed” to make us do so.
______ he referred to in his article was unknown to the general reader.
____ matters most in learning English is enough practice.
Engines are to machines _________ hearts are to animals.