Clothing made of man-made materials has advantage over _________ made of natural ones like cotton, wool or silk.
So difficult ______ it to work with him in the same company that I determined to find another job.
Only when you have finished your homework ______ go home.
It was in the street ______ I live that I met Mr. Green.
A man may usually be known by the books he reads _______ by the friends he keeps.
There are so many books! It is not easy for us to decide what to take and what to_______.