当工作接地电阻不超过４Ω，每处重复接地电阻不得超过（）。
A、4
B、5Ω
C、8Ω
D、10Ω
参考答案：D
_______ that he made an obvious mistake, Jeff went on with his speech.
A．Not realized
B．Not to realize
C．Not to have realized
D．Not realizing
直流锅炉给水质量标准要求给水硬度（）。
A.接近于零
B.不大于10μmol/L
C.不大于0.3μmol/L
