ArrayList list merge_collections, C#

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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Collections;

namespace Rextester
{
    public class Dog
    {

private string _firstName;
        private string _lastName;
        private string _breedName;
        public Dog(string breed,string fname,string lname)
        {
            _firstName=fname;
            _lastName=lname;
            _breedName=breed;
        }

public string first_Name
        {
            get{return _firstName;}
            set{_firstName=value;}
        }
        public string last_Name
        {
            get{return _lastName;}
            set{_lastName=value;}
        }
        public string breed_Name
        {
            get{return _breedName;}
            set{_breedName=value;}
        }
        public string full_Name
        {
            get{return _firstName+" "+_lastName;}
            
        }
        public string breed_And_fullName
        {
            get{return full_Name+" "+_breedName;}
            
        }
    }
   public class Program
    {
        public static void Main(string[] args)
        {
            ArrayList days=new ArrayList();
            days.Add("Sunday");
            days.Add("monday");
            days.Add("Tuesday");
            days.Add("Wednesday");
            days.Add("Thursday");
            days.Add("Friday");
            days.Add("Saturday");

ArrayList months=new ArrayList(days);
            months.Add("Jan");
            months.Add("Feb");
            months.Add("mar");
            months.Add("april");
            months.Add("may");
            months.Add("june");
            months.Add("july");

ArrayList digs=new ArrayList(months);
            digs.Add(100);
            digs.Add(200);
            digs.Add(300);
            digs.Add(400);
            digs.Add(500);
            digs.Add(600);
            digs.Add(700);

ArrayList mix=new ArrayList(digs);
            mix.Add(1);
            mix.Add("Baba Budan");
            mix.Add(new Dog("Bull Dog", "Paul", "breezer").breed_And_fullName);
            foreach(object ob in mix)
            {
                Console.WriteLine(ob);
            }
           
            Console.ReadLine();
        }
    }
}

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Compilation time: 0.06 sec, absolute running time: 0.08 sec, cpu time: 0.08 sec, average memory usage: 22 Mb, average nr of threads: 5