关于蓄能器，下列各项中不正确的是（）。

A．蓄能器中禁止充氧气或空气

B．至少每6个月检查1次其中气体压力

C．需用支架固定，但不能用焊接固定

D．以油口向上垂直安装为宜

I      when I was not at home.I don’t know       the hedge.[ ]

A. was climbing;what happened to

B. climbed;how happened to

C. was climbing;what happens

D. climbed;what happened