单项选择题
A.< 0.65B.为0.60C.< 0.55D.< 0.50
A.< 0.5B.0.50~0.55C.0.55~0.60D.0.60~0.65
A.2.3~2.8B.1.8~2.2C.2.85~3.20D.3.3~3.7