The first indication is that Tuesday afternoon's crash occurred after the metro system staff had switched to manual scheduling following a signal failure.
暗示星期二下午这场事故发生的第一个信号就是，地铁系统员工在信号指示失败后立刻转为手动操作。
2
First used to signal that someone wants to be called back because of lack of credit, it has become a free messaging system.
这种方式最初是用于传达某人由于手机欠费而希望被召回的信息，如今它已成为了一个免费的通讯系统。
3
Chaotic signal generator is one chaotic system which is the first part of chaotic communication and secret communication system.