Mr. Blake __________my letter, otherwise he would have replied by now.

—What's the matter with the man hanging his head there?—Well，if you ________ know, he was caught stealing my bike. 

—Who do you suggest ________ sent to take part in the final competition on behalf of our school?—Jack, I think. 

__________ it rain, the crops_____________.

If he had started at nine o’clock,he       have been in London by eleven o’clock.