a、b两点间电压保持不变，某同学用一只非理想电压表并联在电阻R1两端时，读数为4.3V；用这只电压表并联在电阻R2两端时，读数为4.5V；则ab间的电压一定( )
A．等于8.4V
B．等于8.8V
C．大于8.8V
D．小于8.8V
答案：C
题目分析：电压表与R1并联的时候，相当于R1上又并联了一个电阻，那么相当于R1电阻变小，所以R1分到的电压要比原来小了，测得的电压4.3V要小于R1与R2串联时实际电压；测R2时同理，假设电压表示数为U，因R1和R2测到的电压都要比实际电压小，那么测到的总电压一定小于总电压U，即4.3V +4.5V <U，即a、b间的电压一定大于8.8V，所以C正确。
Maria was born in Peru（秘鲁）.She grew up in a small village. She 46 when she was six years old. She went to elementary school，but she 47 to high school. Her family was very 48 ，and she had to go to work when she was thirteen years old. She 49 in a shoe factory. When Maria was seventeen years old，her family 50 to the United States. First they lived in Los Angeles，and then they moved to San Francisco. When Maria 51 in the United States，she was not very happy. She missed her friends in Peru，and she didn’t 52 a word of English. She began to study English at night， 53 worked in a factory during the day. Maria studied very hard，and now she speaks English well. She’s still 54 at night，but now she’s studying typing. She wants 55 a secretary. Maria still misses her friends. But she’s very happy now，and she hopes she will have a good future（将来）in the new country.
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