Not until he took off his sunglasses _______ him.

_______ are the days when girls were looked down upon.

_______ about wild plants that they decided to make a trip to Madagascar for further research.

The research is so designed that, once _______, nothing can be done to change it.

I can’t quite remember ______you started doing the work

It was in the street where a serious accident happened last week ______another happened yesterday.

If the weather is fine, we’ll go. If ______, ______.

Only by practising a few hours every day ________ be able to play the piano well.

Though ______in a big city, Peter always prefers to paint the beautiful scenes of country     life.

________ you ought to do now is to see a doctor at once.