一维数组怎么给二维数组赋值

一维数组如何给二维数组赋值?
一维数组string[] a1 = new string[91];
二维数组string[13,7] a2 = new string[13,7];
请问如何用a1把a2填充满

------解决方案--------------------
C# code

            string[] a1 = new string[91];
            string[,] a2 = new string[13,7];
            int k = 0;
            for (int i = 0; i < 13; i++)
            {
                for (int j = 0; j < 7; j++)
                {
                   a2[i, j] = a1[k];
                   k++;
                }
            }