用所给词的适当形式填空
What          (drive) the workers to work hard from morning till night?
When you speak English, you should try your best to make yourself
         (understand).
We'd better keep the fire           (burn) so that it can keep us warm.
I am sorry to have kept you          (wait) such a long time.
When the police got to the place, they found the boy          (lie) on the ground.
She is the only one of these girls who          (play) bridge well.
Neither Peter nor his parents          (be) at home.
Every means        (be) tried but without much result.