Not until the train pulled into the station          that his suitcase was gone.

A．did he find

B．had he found

C．he had found

D．he found

危险源的风险评价通常采用D=L×E×C来进行判断，该种方法称为（）。

A.头脑风暴法

B.德尔菲法

C.作业条件危险评价法

D.事故树法