运行中的锅炉发现尾部再燃烧时，应（），停用送风机、吸风机。严密关闭烟道挡板、人孔门、看火门及热风再循环门等，防止（）漏入炉内。打开灭火装置的进汽（水）阀，送入蒸汽（水）进行灭火。

There comes a time in every man's life_____.

A．that he needs to think

B．when he has to think

C．therefore he has to work hard

D．then he will need it