—Let’s go out for a walk.—You’d better not. These days the air is getting much ________ than it was before.
The harder we work, the ___ result we will get.
If you want to do better in playing the piano, you need more ____.
Willie will learn swimming, no matter how much it ____.
---May I use your dictionary? ---_____.
He was so tired that he fell asleep ___he went to bed.