This problem may lead to more serious ones if _____ unsolved.
Collecting stamps as a hobby___________ increasingly popular during the past fifty years.
The train was__________ to arrive at 11:30,but was an hour late.
Can you imagine what a girl will look like___________ she comes across a rat in her room?
--It starts raining outside.--Oh, ____________!
He felt rather __________ that she should drive the car at such a____________ speed.