The physics teacher once said that we first _____the lightning followed by thunders because light ______ faster than sound.
Now there is a danger _________ the ground may fall under the heavy traffic.
We think it possible _________ the local government will be able to solve the housing problem.
She took it for granted _________ I'd be back home an hour later.
_________ caused the accident is still a complete mystery.
It is widely _________ that smoking can cause cancer.