对于常见的可燃液火、电气火以及可燃固体表面火,气溶胶灭火剂灭火效能在()g/m3之间。
A.40~50
B.50~60
C.40~60
D.50~70
参考答案:C
程控交换机的扫描指令,驱动指令包含的内容与功能有何不同?
More and more students are going to have Friday afternoons________ to volunteer and help others.
A.at
B.in
C.on
D.off