We can’t work out the physics problem. Can you tell us _________?
.—_____ you _____ your homework yet? —Yes, I _____ it ten minutes ago.
You’d better speak aloud ______ we can hear you.
—It’s very hot, but quite wet today. —_____
Now most families have only one child _____ our country’s one-child policy.
There are fifty students in our class, _____ of us _____ football.