—May I go and play with Dick this afternoon,Mum?—No,you can’t go out________your work is being done.
Experiments of this kind __________ in both the U. S. and Europe well before the Second World War started.
After the explosion, every means __________ prevent the river from __________.
We students should __________ ourselves __________ knowledge, for the competition nowadays is very fierce.
He is really considering __________ himself to __________ these children of the poor mountain village.
Linda's parents died when she was a baby, and she was __________ by her aunt.