单项选择题
A.节流 B.回流 C.变速 D.间断运转
A.ⅠⅡ B.ⅡⅢ C.ⅡⅣ D.ⅠⅡⅢ
A.15%/12%~17% B.30%/20%~30% C.40%/50%~70% D.60%/30%~40%