A.均勻 B.不均勻 C.沒影響 D.有時(shí)均勻有時(shí)不均勻
A.D≥12d B.D≥14d C.D≥16d D.D≥18d
A.D≥15d B.D≥16d C.D≥17d D.D≥18d