下列哪些是选择电缆敷设路线的原则（）。
A、长度最短
B、便于敷设
C、便于维修
D、以上都是
参考答案：D
We got in my father's car and headed straight home and__________,I surely would have been stuck in the station for several days.
A．had I not
B．did I not
C．if I didn't
D．if I had
霍乱发病主要由哪项引起
A．肠毒素B．细胞毒素C．神经毒素D．内毒素E．类毒素
