-Is there any flight to New York today?--I think there ____ be, for the weather is too bad.A mustn’t B may not C shouldn’t D can’t
In that month, he earned as much as, if ____ than, $40 000.
The research is so designed that once _____ nothing can be done to change it.
If _____ carefully, the experiment will be successful.
He is a man of few words, and seldom speaks until _____ to.
They kept trying _____ they must have known it was hopeless.