问题
填空题
在输出电压平均值相等的情况下，三相半波整流电路中二极管承受的最高反向电压是三相桥式整流电路的（）倍。
答案
参考答案：2
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在输出电压平均值相等的情况下，三相半波整流电路中二极管承受的最高反向电压是三相桥式整流电路的（）倍。
参考答案：2
| 阅读理解。 |
| George Stephenson was born in 1781 in a poor family. He had to start work when he was only eight. When George was fourteen, he became his father's helper. He spent a lot of time learning about engines (发动机). And on holidays he often made one engine to pieces and studied each piece carefully. Soon he became a very good worker though he could not read or write. He began to learn English letters when he was seventeen years old. Every day after he did twelve hours of hard work,he walked a long way to have lessons from a young school teacher. On his eighteenth birthday, he wrote his own name for the first time in his life. George invented (发明) many things in his life. The train was the greatest one among them. Today when we take trains from one place to another, we'll think of this great man-George Stephenson. |
| 1. In which year did George Stephenson start to help his father? ______. |
[ ] |
| A. In 1781 B. In 1789 C. In 1795 D. In 1798 |
| 2. He learned about the engine ______. |
[ ] |
| A. through reading and writing B. by making it to pieces and studying each piece carefully C. at lessons from a young teacher D. by asking a lot of questions |
| 3. He spent a lot of time learning about engines and soon he became ______. |
[ ] |
| A. a great man B. a good maker C. a good worker D. a good student |
| 4. George Stephenson invented the ______. |
[ ] |
| A. the train B. the telephone C. the car D. the computer |
| 5. From the passage we know George Stephenson was one of the greatest ______ in the world. |
[ ] |
| A. workers B. writers C. learners D. inventors |
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