单项选择题
A.5~13B.20~25C.30~35D.40~50
A.0.1%~0.2%B.0.2%~0.4%C.0.4%~0.6%D.0.7%~1.2%
A.冲天炉B.感应炉C.冲天炉与感应炉双联D.电阻炉