单项选择题
A.≤0.15%B.≤0.20%C.≤0.30%D.≤0.40%
A.≤0.85%B.≤0.45%C.≤0.55%D.≤0.65%
A.1.8~2.2B.6.8~7.2C.7~9D.2.8~3.5