—— Hurry up. The bus is coming! —— Oh, no, we mustn’t cross the street ______ the traffic lights are green.
Our teacher told us that the sun ______ the earth light.
If you ask him _____, he will be happy to help you.
We all know travel can ______ our knowledge of the world.
Vera is ______ in English class. She puts up her hand every time her teacher asks a question.
I don’t know his ______, so I can’t write to him.