Tom had to have his car repaired in a garage because it______seriously.
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.