Mr. Smith gradually _____ a knowledge of the subject.
—Can I pay the bill by check? —Sorry, sir.But it is the management rules of our hotel that payment ____ be made in cash.
What I want to know is ______ he likes the gift given by us.
—Waiter! — —I can’t eat this. It’s too salty.
The poet and pianist is going to give us a talk this afternoon.
We can never expect ____ bluer sky unless we create _____less polluted world.