单项选择题
A.10%B.0.1%C.0.45%D.4.5%
A.0.1%B.0.2%C.1%D.1.2%
A.Wc≤0.0218%B.0.0218%< Wc≤2.11%C.2.11%< Wc≤6.69%D.Wc≥6.69%