加热炉停煤气操作时，先关闭煤烧嘴的（）阀门后关煤气总阀门。
A.空气阀门
B.氮气
C.煤气
参考答案：C
The guests were _________ in the front rows ________ to the president attentively.
A．seating; listened
B．seating; listening
C．seated; listened
D．seated; listening
Oracle服务器由Oracle______和Oracle实例两部分组成。
