Lực hấp dẫn do trái đất tác dụng lên mặt trăng F1 và do mặt trăng tác dụng lên trái đất F2 có đặc điểm gì

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1. It was such an interesting novel that I read it many times. (enough) -> The novel was......................... 2. To spend all that money was a shame. (it) ->We consider ......................... 3. He is supposed to help his parents with housework. (duty) -> It's his....................... 4. She last saw him years ago. -> It's years.............. 5. "Helen wrote that poem, not Mary," said he. -> According to him, it was..................... 6. Mary keeps a pig in her garden. -> What Mary........................ 7. My secretary sent the bill to Mr. Pike yesterday. -> It was my secretary.................................. 8. Collin went to London on Tuesday to see Mary. -> To see Mary was________________ 9. Many of the applicants he interviewed were very well-qualified. -> He...................................... 10. I received a letter urging me to pay the account at once. -> The letter................................... 11. I was extremely grateful for the wonderful present. (which) -> It was.....................................I was extremely grateful. 12. My father reads most of the local newspapers and also gets a lot information from the Internet in order to try to keep himself ............. A. well-informed B. intelligent C. wise D. determined 13. Their requirement _____4 languages was unreasonable. A. speaks B. speak C. to speak D. speaking 14. I'm not used to living in a city with a high crime rate. -> This is the first time....................................... 15. The government should really do something about air pollution.(time) -> It's .......................................about air pollution.