氧气瓶应设有防振圈和安全帽。
参考答案：对
I wanted to buy a storybook but there were______ left in that bookstore．
A．anyone
B．no one
C．none
D．nothing
废气锅炉吹灰应尽量在（）时进行。
A.主机低负荷
B.主机高负荷
C.废气锅炉低汽压
D.废气锅炉高汽压
