Tom, clean up the broken glass _________ someone walks on it.
—Jack can't concentrate on his lessons recently.—Yes, that might ____ why he did so badly in the last test.
They two free tickets to Australia, otherwise they’d never have been able to afford to go.
Not until they left school how much their teachers loved them and helped them.
This new kind of chemicals will help keep the air, soil and water________ from pollution.
---I have cleaned the room three times a day. Look, It is a mess again. --- ! Wait until the children go to bed.