Mở rộng một khu đất hình thang vẫn giữ nguyên chiều cao và đáy lớn ta được khu đất hình vuông có diện tích 81m2. Sau khi mở rộng, diện tích khu đất tăng thêm 6,3m2 . Tính đáy nhỏ của hình thang đó.

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Exercise 6: Choose the best answer. 1. I’m not an astronaut. If I _________ an astronaut, I ________ my camera with me on the rocket ship. A. am/ will take B. was/ would take C. were/ had taken D. was/ would have taken 2. Don’t throw aerosol into a fire. An aerosol ________ if you _______ it into a fire. A. will be exploded/ throw B. would explode/ threw C. explodes/ will throw D. can explode/ throw 3. That sounds like a good offer. I ________ it if I ________ you. A. had accepted/ were B. will accept/ am C. would accept/ were D. accepted/ were 4. Nora is using my car right now. Is she ________ it back in time, you’re welcome to borrow it. A. brought B. would bring C. will bring D. brings 5. If energy ________ inexpensive and unlimited, many things in the world ________ different. A. is/ will be B. was/ would be C. had been/ would have been D. would be/ were 6. If you _______ all of my questions, I _______ anything to help you. A. don’t answer/ can’t do B. didn’t answer/ won’t do C. wouldn’t answer/ can’t do D. wouldn’t answer/ couldn’t do 7. If I _______ wings, I ______ take an airplane to fly home. A. have/ won’t have to B. had/ would have to C. have/ will have to D. had/ wouldn’t have to 8. - Here’s my phone number. - Thanks. I ______ give you a call if I _______ some help. A. will give/ will need B. would give/ needed C. give/ need D. will give/ need 9. If we ______ serious about pollution, we ______ more money to research. A. had been/ spent B. were/ had spent C. were/ would spend D. are/ will spend 10. Sea water is salty. If the oceans ______ of fresh water, there ______ plenty of water to irrigate all the deserts in the world. A. consisted/ would be B. consisted/ were C. would consist/ could be D. consist/ will be