【名词&注释】
均方根值(root mean square value)、轮发电机组(turbine power generating sets)、普通碳素钢(plain low carbon steel)、轴承座振动(vibration of bearings)
[单选题]普通碳素钢的含硫量不大于()%,含磷量不大于()%
A. 0.055,0.045 B. 0.045,0.04 C. 0.05,0.06 D. 0.045,0,05