By the time the fire-fighters arrived, the fire had been put＿＿＿by the teachers and the students.

A．down

B．away

C．out

D．off

通过承担多个风险，使相关风险能够互相抵消的方法是（）。

A.情景分析

B.集中趋势法

C.失效模式与影响分析

D.风险对冲