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问题 单项选择题

变频器的频率范围是指变频器输出的最高频率fmax和最低频率fmin，通常（）。

A、最低工作频率为0.1~1Hz

B、最低工作频率为5~20Hz

C、最高工作频率为100~200Hz

D、最高工作频率为50~100Hz

答案

参考答案：A

完形填空

阅读下面短文．按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用括号中词语的正确形式填空。

A young man, while traveling through a desert, came across a spring of clear water.   小题1:___water was sweet. He filled his leather container so that he could bring some back to an elder 小题2:__  had been his teacher. After a four-day journey, the young man  小题3:   ( present ) the water to the old man. His teacher took a deep drink, smiled   小题4: ( warm ), and thanked his student very much for the sweet water. The young man went home   小题5:  a happy heart.

After the student left, the teacher let   小题6: student taste the water. He spit it out,    __小题7:___(say) it was awful. Apparently, it was no longer fresh because of the old leather container. He asked his teacher, "Sir, the water was awful. Why did you pretend to like   ____小题8:__ ?" The teacher replied,  " You tasted the water. I tasted the girl. The water was simply the container for an act of kindness and love. Nothing could be  小题9:__  (sweet). "

We understand this lesson best  小题10: we receive gifts of love from children. Whether it is a cheap pipe or a diamond necklace, the proper response is appreciation. We love the idea within the gift rather than the thing.
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填空题

在△ABC中，若∠C=80°，∠A-∠B=20°，则∠B=______．
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