单项选择题
A.1B.2C.3D.4
A.40%~60%B.50%~60%C.50%~70%D.70%~85%
A.4000V/m,2V/mB.5000V/m,1.8V/mC.4000V/m ,1.1V/mD.5000V/m ,1.5V/m