He has written a book_______I have forgotten.
—How long are you staying? —I don’t know. ______.
Whatever work you are doing, you should concentrate your attention ______it.
The incomes of skilled workers went up. _____, unskilled workers saw their earnings fall.
______in a proper way, waste can be turned into useful things.
It’s helpful to put children in a situation______ they can see themselves differently.