单项选择题
A.2/1和2/2 B.1/1、2/1和2/2 C.1/1和2/1 D.1/1和2/2
A.顺、逆和逆 B.顺、顺和逆 C.顺、顺和顺 D.逆、顺、逆
A.50mpm B.80mpm C.70mpm D.60mpm