单项选择题
A.生石灰 B.叶蜡石 C.纯碱 D.高岭土
A.97% B.95% C.98% D.96%
A.先关燃气再关氧气 B.先开燃气再开氧气 C.先关氧气再关燃气 D.先开氧气再开燃气
A.20% B.30% C.40% D.50%
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