单项选择。 1. _____ as much as one-fifth of all timber harvested is not used. A. The estimate B. They estimate C. They are estimated D. It is estimated that 2. _____ was once regarded as impossible has now become a reality. A. That B. Which C. Who D. What 3. _____ we have achieved is attributed to the guidance of our parents. A. Whoever B. Whatever C. However D. That 4. _____ you say now can’t make up for what you’ve done. A. No matter B. Whatever C. However D. That 5. Although _____ happened in this developed country sounds like science fiction, it could occur elsewhere in the world. A. which B. what C. how D. it 6. _____ she had forgotten to take her notebook. A. That occurred to her B. She occurred that C. To her that occurred D. It occurred to her that 7. I am sure that _____ she said is wrong. A. which B. all C. this D. what 8. We lost our way in the forest, and _____ made matters worse was that it was getting dark. A. that B. which C. it D. what 9. _____ occurred to him that he had forgotten to lock the door when he left home. A. This B. It C. That D. These 10. _____ or not is still uncertain. A. He’s coming B. If he is coming C. That coming D. Whether he’s coming 11. It’s _____ he’ll be able to come. A. doubt whether B. doubtful C. doubt it D. doubtful whether 12. It is _____ that the bridge has existed for more than three centuries . A. appeared B. risen C. said D. born 13. _____ he saw both surprised and frightened him. A. That B. When C. What D. Which 14. _____ is a spell of warm sunshine. A. What do we all need B. What all we need C. What we need all D. What we all need 15. _____ is a pity that he failed in the race. A. What B. That C. He D. It 16. _____ a spoonful of soil can tell us so much about the structure and early history of the moon. A. Remarkable B. Quite remarkably C. It is remarkable that D. It is remarkable 17. _____ you nominate will be elected. A. Who B. Which C. Whomever D. That’s 18. _____ book you borrow must be returned within a week. A. What B. Which C. Whichever D. That’s 19. _____ is troubling me is that I don’t have much experience in international commerce. A. It B. That C. Which D. What 20. _____they wil go there to try another experiment has not been decided yet. A. Whether B. If C. About whether D. Why