如图所示，三个电压表用满偏电流相同的电流表改装而成，已知电压表V1的示数为8v，电压表V3的示数为5V，则关于电压表V2的示数，下列判定中正确的是（ ）
A．电压表V2的示数必为3V
B．电压表V2的示数必为5V
C．若三个电压表量程相同，则电压表V2的示数必为3V
D．即使三个电压表量程相同，电压表V2的示数也可能不等于3V
A、B，电压表V2与电阻串联，串联的总电压等于V3的示数5V，所以V2的示数必定小于5V，由于三个电压表量程关系未知，无法确定其示数．故AB错误．
C、D，三个电压表用满偏电流相同的电流表改装而成，满偏电流相等，若电压量程相同，则三个电压表的内阻相等，设为R．
通过电压表V2的电流为I2=I1-I3=
-U1 R
=U3 R
=U1-U3 R 3 R
电压表V2的示数为U2=I2R=3V．故C正确，D错误．
故选C
Passage One
| My First Experience with AIDS Patients 我初次接触艾滋病人 by Marc Kielburger I was ushered to the AIDS ward of a hospice in the slum.I would later learn that the ward did not exist，at least not officially.Not a single person in Thailand had AIDS，according to the Thai government at the time.People got"sick，"of course，sometimes"very sick."but no one had AIDS.The hospice was home to an ever-growing number of"very sick"people. I entered the ward and was greeted by two Thai nurses. "Thank goodness you are here，Marc，"said the first. "You’re a doctor，right " I shook my head. "So you are a medical student then!" I shook my head again. "But you know medicine，right " "Kinda，"I offered."I watch E.R.,every Thursday" After a rapid exchange in Thai，the first one said，"NO problem.Get ready for your fou- hour medical school training!" "But in my country medical school takes years!" I protested. "We don’t have that long," she replied. "So we better get started. " During the next few hours, I learned to clean wounds, administer IVs, treat bedsores, and dispense medicine. The work was punishing, made worse by stifling heat, frequent blackouts, and an incredible stench in the air. I tried desperately to hide my weak nerves and queasy stomach, but more than once dashed for the bathroom to throw up. Just when it seemed my training was coming to an end, the nurse took me aside. "There are only two more things you need to know," she said. "On the left-hand side of the ward, you will find what we call the Exit Area. " As it turned out, she meant "exit" in the largest sense of the word. Terminally ill patients were hidden behind a curtain and then exited out of the ward after death. "The second thing you need to know," she continued, "is that we haven’t had a day off in three weeks. You’ll be looking after the ward by yourself for the next shift. " My jaw dropped. "Don’t worry, Mare," said the other nurse, patting me on the shoulder before turning to leave. "Think of this as the beginning of your residency !" And with that, they walked out. Alone and petrified, I tried unsuccessfully to keep calm. I counted to twenty-four. That’s how many AIDS patients were in my charge. What am I going to do I thought. What can I do I fell back on my training with the Canadian government and put my talents to work. I served patients water-some with ice, some without. Next, I tried to cheer up everyone, myself included, giving enthusiastic high-fives to patient after patient. Soon enough, everyone was laughing. Some were laughing with me, others most definitely at me, but I didn’t care. As long as I could keep people smiling, I was sure it would all be fine. And it was. Until a short while later, when a patient in the Exit Area began to choke. He had fluid in his lungs and could not breathe. As I crossed the floor, I could hear the man gasping for air. Fumbling and scared, I pulled back the curtain and administered the medicine the nurses had recommended. The man didn’t respond. With nothing left to offer, I sat down and held his hand, looking into his eyes as he breathed heavily for a while and then stopped. Watching him slip away, I was hit by a feeling of anguish such as I’d never felt, either before or since. It haunts me to this day. |
Judging from the passage, what is the writer most likely to be
A．A doctor
B．A medical student
C．A volunteer
D．A government official