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duong12345hn
2 năm trước
Cho chóp sabcd có đáy abcd là hình chữ nhật.ab =a,sa=bc=2a (SAC) và (SBD) cùng vuông góc với (ABCD) a) thể tích sabcd b) góc giữa hai (SBC) và (ABCD) c)d(AC;AD) Ai giúp mình với nhé
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Helen Keller was a very bright and beautiful girl. At the age of six months she could already say a few words. But before she was two years old, she was badly ill. She could not see or hear, and soon she could not even talk. Since then Helen had to fight for what she wanted. When she was six, her parents invited a teacher for her. With the help of the teacher, she began to see and hear the world around her through her hands. She learned to read the books for the blind. The teacher took Helen for long walks, and told her about all the beautiful sights. Helen touched flowers, climbed trees and smelt a storm before it came. She also learned how to swim and ride a horse. After she grew up, she became a famous writer in America. Her first and most famous book is The Story of My Life. Her story brought new hope to many blind and deaf people. It gave light to those in darkness and encouraged them to live and work. 1. When could Helen Keller already say a few words? A. at the age of two B. at the age of a year and a half C. at the age of six months D. when she was six years old 2. Why couldn't Helen see or hear later? A. Helen was badly ill. B. She had a traffic accident. C. Helen was very tired. D. She became very lazy. 3. How could Helen begin to see and hear the world around her? A. with the help of her father B. through her feet C. with the help of her parents D. with the help of her teacher 4. After Helen grew up, she became a famous …………………. A. doctor B. scientist C. singer D. writer 5. What gave light to those in darkness and encouraged them to live and work? A. their teacher's help B. Helen's story C. their parents' help D. Helen's songs

Scientists are trying to make the deserts into good land again. They want to bring water to the deserts, so people can live and grow foods. They are learning a lot about the deserts. But more and more of the earth is becoming deserts all the time. Scientists may not change the desert in time. Why is more and more land becoming deserts? Scientists think that people make deserts. People are doing bad things to the earth. Some places on the earth don't have very much rain. But they still don't become deserts. This is because some green plants are growing there. Small green plants and grass are very important to dry places. Plants don't let the hot sun make the earth even drier. Plants don't let the wind blow the soil away. When a little rain falls, the plants hold the water. Without plants, the land can become a desert much more easily. 1. According to the passage, deserts …………………. A. can all be turned into good land soon B. never have any plants or animals in them C. get very little rain D. are made by people 2. The underlined word "They" in the passage refers to …………………. A. scientists B. deserts C. people D. foods 3. Small green plants are very important to dry places because ………………… A. they develop together with grass B. they let the sun make the earth even drier C. they don't help to hold the water D. they don't let the wind blow the earth away 4. Land is becoming deserts little by little because …………………. A. there is not enough rain B. people don't do what scientists wish them to do C. plants can't grow there D. scientists know little about the deserts 5. After reading this, we learn that …………………. A. plants can keep dry land from becoming deserts B. it is good to get rid of the grass in the deserts C. all places without much rain will become deserts D. it is better to grow crops on dry land than to grow grass

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