C#

using System;
using System.Collections.Generic;

namespace ConsoleApplication1
{
   class Program
   {
      static List<int> listA = new List<int>();
      static List<int> listB = new List<int>();
      static List<int> listC = new List<int>();
      static List<int> listOut = new List<int>();

      static void Main(string[] args)
      {
         MakeSortedLists();   //with test data for lists A, B and C
         const int HIGH_VALUE = int.MaxValue; //Dummy value greater than max in any list

         int m = 0;  // listOut index - only need this if listOut is really an array
         int i = 0;  // listA index
         int j = 0;  // listB index
         int k = 0;  // listC index

         int valueA = listA[0];
         int valueB = listB[0];
         int valueC = listC[0];

         while ((valueA < HIGH_VALUE) || (valueB < HIGH_VALUE) || (valueC < HIGH_VALUE))
         {
            if ((valueA <= valueB) && (valueA <= valueC))
            {
               listOut.Add(listA[i]);       //listOut[m] = listA[i] IF listOut is an array
               i++;
               valueA = (i < listA.Count) ? listA[i] : HIGH_VALUE;
            }
            else
            {
               if ((valueB <= valueA) && (valueB <= valueC))
               {
                  listOut.Add(listB[j]);    //listOut[m] = listB[j] IF listOut is an array
                  j++;
                  valueB = (j < listB.Count) ? listB[j] : HIGH_VALUE;
               }
               else
               {
                  listOut.Add(listC[k]);    //listOut[m] = listC[k] IF listOut is an array
                  k++;
                  valueC = (k < listC.Count) ? listC[k] : HIGH_VALUE;
               }
            }
            m++; // only need this if listOut is really an array
         }

         WriteOutList();
         Console.ReadLine();
      }

      static void MakeSortedLists()
      {
         listA.Add(10);
         listA.Add(11);
         listA.Add(2);
         listA.Add(1);
         listA.Add(16);

         listB.Add(5);
         listB.Add(13);
         listB.Add(7);

         listC.Add(10);
         listC.Add(6);
         listC.Add(16);

         listA.Sort();
         listB.Sort();
         listC.Sort();
      }

      static void WriteOutList()
      {
         Console.WriteLine("Posn    Value");
         Console.WriteLine("-------------");
         for (int m = 0; m < listOut.Count; m++)
         {
            Console.WriteLine("{0,3}  >> {1,4}", m, listOut[m]);
         }
      }
   }
}