It is often recommended that children ________chances to get close to nature.

I _____ you somewhere before , but your name has escaped me _____ moment . 

John promised his doctor he ________ not smoke, and he has smoked ever since.

—You just think of yourself! You kept me wailing for at least three hours． —I’ m sorry that you _____ think so．

 —Do you know where the headmaster is? I have something urgent.　　　　—Oh, he ____ have gone far, for the computer is still on in the office.