.Whenever you enter the reading room, you can find all the students _____ at their desks, with their attention _____ on the books, except Tom.
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.