单项选择题
A.30:50~60:20B.30:50~80:20C.50:50~80:20D.50:50~60:20
A.0.005-0.02B.0.005-0.001C.0.05-0.02D.0.005-0.002
A.0.5-0.1B.0.5-0.9C.0.5-0.2D.1.0-0.9