using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        Dictionary<string, string> a = new Dictionary<string, string>() { { "a", "b" } };

        Dictionary<string, string> b = new Dictionary<string, string>() { { "c", "d" } };

​

        var merged = (new List<Dictionary<string, string>>() { a, b }).SelectMany(x => x).ToDictionary(x => x.Key, y => y.Value);

        Console.WriteLine(String.Join(",", merged.Keys));

        Console.WriteLine(String.Join(",", merged.Values));

    }

}