Tìm số nguyên x,y biết a, x² - y²=91 b, x^6 +3x³ +1 =y^4 c, x² + 4x - y² =1

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V. Change the following sentences into the passive voice. 1. The government just widened the park last year. ________________________________________________________ 2. We consider national parks ideal habitats for animals. _______________________________________________________________ 3. They have just planted ten thousand trees in this area. ________________________________________________________ 4. They are opening more national parks in this country. ________________________________________________________ 5. Do you think modern technology is destroying our nature ? ________________________________________________________ 6. We stopped poaching completely after setting up this national park. ________________________________________________________ 7. No one has found out an effective way to protect endangered animals. ________________________________________________________ 8. Should any of us check the baby animals again? ________________________________________________________ 9. The government must ban tusk sales to prevent poachers from killing elephants. ________________________________________________________ 10.People have killed their tigers for skin and bones. ________________________________________________________ 11. We should use public transport means more as a way to protect the environment. ________________________________________________________ 12. Somebody must have shot this poor rhino. ________________________________________________________ 13. The government doesn't allow hunters in national parks. ________________________________________________________ 14. With national parks, we have created safe places for animals and trees to live. ________________________________________________________ 15. They couldn't have killed the baby bear if its mother hadn't been unconscious. ________________________________________________________