Don’t start reading a book ________ you find that it’s one you can read with ease and understanding.
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.
After ______ was about then minutes, the teacher gave the students the correct answer to the question.