I was about to get on the bus _________someone called.
I met the teacher in the street yesterday ____ taught me English three years ago.
It will be quite a long time _____ she is back again, so don't be too cross with her.
I often go to the English corner to have a free talk with my classmates ____ I am busy.
In order to continue to learn by ourselves when we have left school, we must ________ learn how to study in the school now.
Unless they are programmed by humans, computers are nothing more than big pieces of metal. But once _____ what to do, they show extraordinary power in carrying it out.