using static System.Console;

​

public class Program {

    public static void Main() {

        var array2D = new int[,] { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } };

        WriteLine(array2D[0, 0]);

        WriteLine(array2D[2, 1]); //2 (linha) * 3 (total de colunas + 1 (coluna) = 7

        var array1D = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };

        WriteLine(array1D[0]);

        WriteLine(array1D[7]);

        for (int i = 0; i < array2D.GetLength(0); i++) {

            for (int j = 0; j < array2D.GetLength(1); j++) Write($"{array2D[i, j]} ");

            WriteLine();

        }

        for (int i = 0; i < array1D.Length; i++) Write($"{array1D[i]} ");   }

}