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【单选题】
如果对某一闭合曲面的电通量 , 以下说法正确的是A.
S 面上所有点的 必定不为零
B.
S 面上有些点的 可能为零
C.
空间电荷的代数和一定不为零
D.
空间所有地方的电场强度一定不为零
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举一反三
【单选题】有一电阻、电感和电容串联电路，R=600Ω，L=1.911亨，C=5.308μF，电路电压U=220V、ｆ＝50Hz,该电路的电流为。
A.
0.25A
B.
0.3A
C.
0.37A
D.
0.45A
【单选题】It is said that sixty percent of all energy ________ in the world today is being lost as wasted heat.
A.
produced
B.
producing
C.
to produce
D.
having produced
【单选题】Over time, my remaining hearing dropped to 20 percent, where it is today.
A.
Gradually I lost more of my hearing until I was 80 percent deaf, as I currently remain.
B.
Soon I lost 20 percent of my hearing after I moved to where I’m living today.
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