jzj.cs

namespace AcaEstaTuTarea{
  static class Program{

      static void Main(string[] args){
        
        string[] arr1 = {"1","2"};
        
        string[] arr2 = {"a","b","c","d","e"};
        
        string[] arr3 = new string[arr1.Length * arr2.Length];
        
        int count = 0;
        for(int a = 0; a < arr1.Length; a++){
            for(int b = 0; b < arr2.Length; b++){
              arr3[count] = arr2[b] + arr1[a];
              count++;
            }
        }
      }
  }
}