The governments are very cautious about setting a new policy and make no decision _____ they are quite sure it is the right one.
The film star walked to his car, ______ a crowd of journalists.
_______ on time, this medicine will be quite effective.
When I handed the report to John, he said that George was the person _______.
He is a man of few words, and seldom speaks until _______ to.
Though I have often heard this song _______. I have never heard you _______ it.