3/5,3/5,2/3,3/4,()A:17/20,B:19/20,C:21/25,D:23/25

问题描述:

3/5,3/5,2/3,3/4,()A:17/20,B:19/20,C:21/25,D:23/25

化3/5,6/10,10/15,15/20,=(15+6)/25=21/25C"