How to add duplicate keys into the Dictionary

Question

I have some lines from text files that i want to add into the Dictionary.I am using Dictionary for the first time.While adding up starting lines it was Ok but suddenly i got err

Answer 1

Example:

class Program
        {
             private static List> d = new List>();

            static void Main(string[] args)
            {
                 d.Add(new KeyValuePair("joe", 100));
                 d.Add(new KeyValuePair("joe", 200));
                 d.Add(new KeyValuePair("jim", 100));
                 var result = d.Where(x => x.Key == "joe");
                foreach(var q in result)
                    Console.WriteLine(q.Value   );
                Console.ReadLine();
            }
         }