单项选择题

若有以下说明: int a[12]={1,2,3,4,5,6,7,8,9,10,11,12}; char c='a',d,g; 则数值为4的表达式是 ( )

A.a[g-c]
B.a[4]
C.a['d'-'c']
D.a['d'-c]