Pleasant music is often played ________ classes to make students refreshed and relaxed for a while.
Never before ______ so highly successful in his attempts to forecast the weather accurately on a small scale.
There is not much time left, so I won't tell you about it ______ .
The moment we heard the news of the earthquake,we began to ______ the work to rescue those who were trapped in the building.
_____the new fund-raising plan is approved, we will soon have more money to build the gymnasium.
Of all the things I have done in my professional career, nothing has been more ______ than writing that book.