水是最常用的一种天然灭火剂，在灭火中具有（）的特点。

A.高效

B.经济

C.获取方便

D.使用简单

E.快捷

Many of them turned a deaf ear to his advice, _______ they knew it to be valuable.

A．as if

B．even though

C．now that

D．so that