Whenever you are to walk on the ice , that it is solid and safe enough.
He felt _________ when he found a stranger _________ about at the gate of the police station.
____ since the night before, I felt very hungry.
_____ with the accident, he was forced to resign.
They use computers to keep the traffic smoothly.
All flights ________called off because of the terrible weather, they had to go there by train.