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问题 选择题

如图所示的电路中，电源电压不变，移动滑动变阻器R1的滑片P，当电流表的示数变化范围当电流表的示数1A～1.3A时，电压表的示数变化了3V，则该定值电阻R2所消耗功率的变化范围是

A．3 W ～3.9W

B．3W～5.07W

C．3.9W～10W

D．10W～16.9W

答案

答案：D

题目分析：由题意可知R2==ΔU/ΔI=3V/（1.3A-1A）=10Ω，当电流表的示数1A时，R2所消耗功率P2＝I2R=（1A）2×10Ω=10W，当电流表的示数1.3A时，R2所消耗功率P2‘＝I2R=（1.3A）2×10Ω=16.9W。故选D

完形填空

Chinese proverbs are rich and they are still widely used in Chinese people’ daily life.___ 小题1:_ these proverbs there are often interesting stories. For example, the proverb, “plucking up a crop ___小题2:___ (help) it grow”, is based on the following story.

It is said that a short-tempered man in the Song Dynasty(960-1279) was very anxious to help __小题3:___ rice crop grow up quickly. He was thinking about ___小题4:__ day and night. But the crop was growing much slower than he expected.

One day, he came up with an idea __小题5:___ he would pluck up all of his crop a few inches. He did so the next day.

He was very tired __小题6:__ doing this for a whole day, __小题7:__ he felt very happy since the crop did "grow" __小题8:__ (high).

His son heard about this and went to see the crop. Unfortunately the leaves of the crop began to wither.

This proverb is saying we have to let things go in their __小题9:__ (nature) course. Being too anxious to help an event develop often __小题10:__ (result) in the contrary to our intention.
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单项选择题

对轻纺和食品机械上的某些部位，当采用（）润滑时，可有效防止油的滴漏。

A.机械油

B.机床主轴油

C.润滑油

D.齿轮油
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