单项选择题：在linux系统中，修改组的id号使用的命令是（）。A、chmod B、usermod

题型：选择题

已知M（－3，0），N（3，0），|PM|－|PN|=4，则动点P的轨迹是：（）

A．双曲线

B．双曲线左支

C．双曲线右支

D．一条射线

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题型：单项选择题 A1型题

通过不断的学习、环境的影响，人类的行为是在不断发展变化的，这是指人类行为的（）。

A.目的性

B.差异性

C.可塑性

D.主动性

E.被动性

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题型：计算题

电磁炉是一种高效、方便、卫生的新型灶具，为了研究电磁炉，小锋同学首先观察了家中的电能表，看到电能表的铭牌上标有“220V 10A”和“3000r/kW•h”字样．然后小锋关闭了家中其他用电器，只把电磁炉接入电路中，将质量为3kg、初温25℃的水烧开，这个过程中电能表转盘转了900转。已知水的比热容是4.2×10³J/（kg•℃），当时气压为标准大气压．

求：（1）加热过程中水吸收的热量；

（2）电磁炉的消耗的电功多少J；

（3）电磁炉的热效率．

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题型：完形填空

My parents operated a small restaurant in Seattle. It was open twenty-four hours a day, six days a week. And my first real job，when I was six years old，was小题1:the diners’ shoes. My father had done it when he was young，so he taught me小题2:to do it efficiently，telling me to 小题3:to Re-shine the shoes if the customer wasn’t小题4:.

Working in the restaurant was a cause of great小题5:because I was also working for the good of the family. But my father小题6:that I had to meet certain standards to be part of the team. I小题7:to be punctual，hard-working，and polite to the小题8:.

I was小题9:paid for the work I did at the restaurant. One day I made the mistake of advising Dad that he小题10:give me $10 a week. He said，“OK. How about you paying me for three meals a day you have here? And小题11:the times you bring in your friends for free soft drinks?” He小题12:I owed him about $40 a week.

I remember returning to Seattle after being小题13:in the US Army for about two years. I had just been promoted to Captain at that time. And full of pride，I walked into my parents’ restaurant，but the小题14:thing Dad said was，“How about your小题15:up tonight?” I couldn’t小题16:my ears! I am an officer in the Army! But it didn’t 小题17:as far as Dad was concerned，I was just 小题18:member of the team. I reached for the mop. Working for Dad has taught me the devotion to a小题19:is above all. It has nothing to do with小题20: that team is involved in a family restaurant or the US Army.

小题21:A．cleaning shining C．removing D．keeping