A.一次更换 B.双次更换 C.三次更换 D.每次更换
A.每次更换ⅠⅡ端 B.单次更换Ⅰ端 C.双次更换Ⅰ端 D.三次更换ⅠⅡ端
A.每次更换Ⅰ端 B.每次更换ⅠⅡ端 C.双次更换ⅠⅡ端 D.三次更换ⅠⅡ端