已知 a=log52,b=log83,c=12a = {\log }_{5}2,b = {\log }_{8}3,c = \frac{1}{2}a=log52,b=log83,c=21 ，则下列判断正确的是（ ）A. c<b<ac < b < ac<b<a B. b<a<cb < a < cb<a<c C. a<c<ba < c < ba<c<b D. a<b<ca < b < ca<b<c