C语言中对二维数组的正确定义是?

C语言中对二维数组的正确定义是?

选项A：int a[2,3]={1,2,3,4,5,6};

选项B：int a[ ] [3]={1,2,3,4,5,6};

选项C：int a[2] [ ]={1,2,3,4,5,6};

选项D：int a[ ] [ ]={1,2,3,4,5,6};