问题
填空题
交流供电系统可以有三种交流电源（）、（）、（）。
答案
参考答案：变电站供给的市电；油机发电机供给的自备交流电；UPS供给的后备交流电
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交流供电系统可以有三种交流电源（）、（）、（）。
参考答案：变电站供给的市电；油机发电机供给的自备交流电；UPS供给的后备交流电
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| The world is not hungry, but it is thirsty. It seems 1 that nearly 3/4 of the earth is covered with water while we say we are short of water. Why? Because about 97% of water on the earth is sea water which we 2 drink or use for watering plants. Man can only drink and use the 3% of the water that comes from rivers and lakes. And we can't even use all of that, 3 some of it has been dirty. Now more water is needed. The problem is: Can we avoid (避免) a serious water shortage later on? First, we should all learn how to 4 water. Secondly, we should find out the ways to reuse it. 5 have always been making study in this field. Today, in most large cities water is used only once and then 6 to the sea or rivers. But it can be used again. Even if every large city reused its water, still there would not be 7 . What could people turn to next? The sea seems to have the best answer. There is a lot of water in the sea. All that needs to be 8 is to get the salt out of the sea water. This is 9 , but it's already in use in many parts of the world. Scientists are trying to find a cheaper way of doing it. So you see, if we can find a way out, we'll be in no 10 of drying up. |
| ( )1. A. interesting ( )2. A. shouldn't ( )3. A. because ( )4. A. make ( )5. A. Teachers ( )6. A. sends ( )7. A. good ( )8. A. reported ( )9. A. expensive ( )10. A. need | B. strange B. don't B. when B. drink B. Scientists B. moves B. enough B. reused B. cheap B. hurry | C. foolish C. mustn't C. while C. save C. Inventors C. runs C. many C. ended C. hard C. danger | D. correct D. can't D. though D. find D. Explorers D. flies D. more D. done D. easy D. time |