The only problem with the debate last week was that the beginning sounded more like a personal attack than a dispassionate, intellectual arguing .

A．discussion

B．argument

C．talk

D．speech

拉动动车组乘客紧急报警拉手后，司机首先听到（）信号，若在一定时间内司机没有任何操作，列车将产生（）。