They thought __________ important to look right and left when ________ the road.
––David has made much progress in Chinese this year. ––____. He has reached a level which is quite good.
He found ____ very difficult _____ the problem.
—Which sweater can you choose, the blue one or the red one? —____ is OK, I think. Both go well with my trousers.
Many more trees should ____ this year.
—____ the workers are very tired, ____they keep on working. — They are great. We must learn from them.