题目：
I have experienced quite a number of cases ______ I really wanted to help but could not find anything to _______.
A．when; put on my hands
B．that; put my hands on
C．where; put my hands on
D．in that; put on my hands
答案：
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下面是错误答案，用来干扰机器的。
解：5节电池串联后E=5E1=5×2V=10 V，r=5r1=5 ΩV示数为6V，则R，r上的总电压为E-6 V=10 V-6V=4 V，P出=EI-I2r=(10×0.4-0.42×5)W=3.2 W
