Then professor walked onto the platform and seated himself in a chair, ______ for answering questions.
I had hardly got to the office ______ my wife phoned me to go back home at once.
I have heard a lot of good things about you ________ I came back from abroad.
There's no way of knowing why one man makes an important discovery ________ another man, also intelligent, fails.
There are some health problems that, when ________ in time, can become bigger.
In the global economy, a new drug for cancer, ________ it is discovered, will create many economic possibilities around the world.