完形填空。 Many people say that they have seen flying saucers (飞碟) in the sky. 1 can these things be? Some people think that they are spaceships from other planets. Doctors 2 that perhaps they are only a weakness of the eyes. It is possible that they are our own planes 3 very high. Or are they birds with the sun's light on them? But some people say that they have seen them 4 . They have seen beings (人) get off them and walk around. They have 5 to those beings, sometimes in English. People have 6 photos of flying saucers and of these beings. We have seen the photos, but sometimes the people had to take them in a 7 . Children have seen flying saucers, and even dogs have seen them. Perhaps we do not think that the 8 of children, or dogs are important. But school-teachers have 9 seen them and Air Force officers and 10 policemen. Must we not listen to these people? (     )1. A. How (     )2. A. say (     )3. A. rising (     )4. A. fly (     )5. A. flown (     )6. A. received (     )7. A. horse (     )8. A. opinions (     )9. A. often (     )10. A. yet B. What B. prove B. flying B. turn B. gone B. bought B. hurry B. discussions B. hardly B. even C. Which C. know C. risen C. land C. come C. taken C. colour C. suggestions C. also C. so D. Where D. understand D. flown D. move D. spoken D. sent D. way D. needs D. still D. then