中国最早的运河开凿于（）
a、春秋时吴国的部沟
b、战国时魏国的蜂水十二渠
c、战国时秦国的郑国渠
d、秦国的灵渠
参考答案：D
计算低压电网的电能损耗？
I took the wrong train ______, I didn't even know it until half an hour later. [ ]
A. by mistakes
B. by mistake
C. with mistake
D. with mistakes
