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;则值为4的表达式是______。
A.a[g-c]
B.a[4]
C.a['d'-'c']
D.a['d'-c]
正确答案是D