如图甲所示．R为电阻箱（0-99.9Ω）．置于阻值最大位置，Rx为未_爱下问搜题

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问题多选题

如图甲所示．R为电阻箱（0-99.9Ω）．置于阻值最大位置，R_x为未知电阻．（1）断开K₂，闭合K₁，逐次减小电阻箱的阻值，得到一组R，I的值，并依据R，I值作出了如图乙所示的R-

1

I

图线，（2）断开K₂，闭合K₁，当R调至某一位置时，电流表的示I₁=1.0A；保持电阻箱的位置不变，断开K₁，闭合K₂，此时电流表的示数I₂=0.8A．据以上数据可知（安培表内阻不计）（　　）

A．电源电动势为3.0V

B．电源内阻为0.5Ω

C．R_x的阻值为0.5Ω

D．K₁断开、K₂接通时，随着R的减小，电源输出功率一直增大

答案

A、根据E=IR+Ir，得R=

E

I

-r，知图线的斜率等于电源的电动势，所以E=

0.5

0.25

V=2V，纵轴截距表示内阻，所以内阻r=0.5Ω．故A错误，B正确．

C、断开K₂，闭合K₁，当R调至某一位置时，电流表的示I₁=1.0A，有：E=I₁R+I₁r，代入数据解得：R=1.5Ω，断开K₁，闭合K₂，此时电流表的示数I₂=0.8A．则有：E=I₂（R_X+R）+I₂r，解得R_x=0.5Ω．故C正确．

D、K₁断开、K₂接通时，由于R_X等于电源的内阻，因为当外电阻等于内电阻时，输出功率最大，当外电阻大于内电阻时增大，则输出功率减小．所以随着R的减小，电源输出功率一直增大．故D正确．

故选BCD．

完形填空

When I was six, my mother placed me in a 36.________ school. For the next nine years, I 37.______ slept in a room that 38.______ less than 30 other kids in it. So, when I was promoted to senior at the high school for my39.___ year there, I had the greatest 40._____ of rooming with just one other classmate, and the added feature of a semi-private bathroom.
We seniors also had the feature of walking around the 41._____ in special hats, we called senior bonnets, so all the other kids would know we were the 42._____ in the high school. As seniors, we frequently went on field 43._____ outside the campus, including city museums, city hall , colleges and theatres. The highlight was a senior class trip to Washington, D.C., 44.______ we sat in on a session of Congress, 45.______ the monument and many other government sites around the city.
Another 46.____ of being seniors was that many of us on athletic and other extra-curricular teams were elected to high ranking for the year. I had the honor and pleasure of47._____ captain of our state championship swim team, while my roommate was voted48.______ of the drama club.
49.______ services were on a sunny day in June. Each of us had looked forward to this moment for ten years. Now we were going out on our own to complete freedom, and we should have been flooded with joy.50.________, to my surprise, I found myself 51._____, something I hadn’t done for years. I noticed many of my 52.______, usually proud of their macho attitudes, were also wiping away tears. We knew we would never be together again as we were on that graduation day. Our senior year 53.______deep feelings of sadness for our54.______, as well as joy for our emerging into a new world 55.____the school campus.

C．occasionally

B．disadvantage

A．being brought	B．being chosen
C．being taken	D．being realized

C．Volunteering

B．Fortunately

A．began with	B．ended with
C．bargained with	D．associated with

多项选择题

下面所列钢筋混凝土工程量计算规则中，正确的有（）。

A.构造柱的工程量，与墙身嵌接部分并入墙身的工程量内计算

B.无梁板下的柱，柱高从柱基上表面算至柱帽的下表面

C.框架柱，柱高从柱基上表面算至上一层楼板的下表面

D.框架柱无楼层者，柱高从柱基上表面计算至柱顶

E.有梁板下的桩，柱高从柱基上表面算至上一层楼板的上表面