He made another wonderful discovery, _______ of great importance to science.
| A．which I think is | B．which I think it |
| C．which I think it is | D．I think which is |
---I’m afraid I ______ return the book to you before Friday.
--- Take your time.
| A．must | B．may | C．needn’t | D．can’t |
. Not until _______ smoking ________ healthy lungs.
| A．did he five up, he had | B．did he give up, did he have |
| C．he gave up, he had | D．he gave up, did he have |
. If it _____ sunny, we _______ a picnic. But it is raining now.
| A．had been, could have had | B．were, could have |
| C．had been, had | D．is, could have |
Many Chinese students find it difficult to remember English words, _______ Yang Mei is an example.
| A．for those | B．in those | C．of whom | D．for whom |
It was easy for her to learn French because _______ of her parents spoke the language.
| A．none | B．neither | C．both | D．all |