单项选择题
A.20m ×20mB.30m ×30mC.40m ×40mD.50m ×50m
A.0.1%~0.2%B.0.2%~0.3%C.0.3%~0.4%D.0.4%~0.5%
A.2B.2.5C.3~5D.6