He had to pause from time to time to wipe the sweat from his forehead, because the air—conditioning system ______________.
The plan _____ by the Chinese government ____ rejuvenating the nation by relying on science.
---I apologized for_____ to tell you when and where the meeting will be held in advance.
Most birds find it safe to sleep in the trees, but _____ they have eggs or young chicks, they don’t use a nest.
---What were you doing when Tom came to see you? ---I had just put on my overcoat and_____ to visit my friends.
As ______along the river bank, she was singing a pop song.