智能终端的两根通信线是没有级性的，正负可以随便接。
参考答案：对
(2013·长沙高考模拟)I ________ him in time, otherwise he would have fallen off the bike.
A．had supported
B．supported
C．have supported
D．support
当电网停电后，矿井监控系统必须保证正常工作时间不小于多少小时？
