Check out example codes for "combine two arraylist c#". It will help you in understanding the concepts better.

Code Example 1

class Program

    {
        static void Main(string[] args)
        {
            ArrayList CountryList1 = new ArrayList();
            ArrayList CountryList2 = new ArrayList();

            CountryList1.Add("Pakistan");
            CountryList1.Add("Nepal");
            CountryList2.Add("Butan");
            CountryList2.Add("Srilanka");
          
            CountryList1.AddRange(CountryList2);
        }

    }

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