消防员防护用品包括（）。
A.消防钩
B.消防锨
C.消防服
D.消防桶
参考答案：C
He didn’t know __________
A．what kind of snake it is
B．what kind of snake is it
C．what kind of snake it was
D．what kind of snake was it
发电机气体置换，所用的介质容积基本上等于发电机的内部气体容积。
