The Array.Rank on C# -

i'm studying array. wondering array.rank, here example:

using system;  public class example {    public static void main()    {       int[] array1 = new int[10];       int[,] array2= new int[10,3];         int[][] array3 = new int[10][];         console.writeline("{0}: {1} dimension(s)",                          array1.tostring(), array1.rank);       console.writeline("{0}: {1} dimension(s)",                          array2.tostring(), array2.rank);       console.writeline("{0}: {1} dimension(s)",                          array3.tostring(), array3.rank);    } } // example displays following output:  //       system.int32[]: 1 dimension  //       system.int32[,]: 2 dimension  //       system.int32[][]: 1 dimension 

my question is: why array3.rank return 1 dimension not 2?

system.int32[][] is 1 dimension, array of array, not 2d array : system.int32[,]