单项选择题
A.≤0.020%(wt)B.≤0.025%(wt)C.≤0.030%(wt)
A.≤0.020%(wt)B.≤0.030%(wt)C.≤0.025%(wt)
A.≤0.030%(wt)B.≤0.035%(wt)C.≤0.040%(wt)