Prof. Richard was crazy about his research. His illness_________ his many years of hard work and irregular diet.
It's nearly seven o'clock . Jack _____ be here at any moment .
If you _____ stop smoking , you can only expect to have a bad cough .
.—Must I turn off the gas after cooking ? --Of course . You can never be ___ careful with that.
“Where is it?” “Where is _____? I don't know what do you mean?”
An awful accident, however, _____occur the other day.