有关random的简单问题

本人对oop不是很了解，做了一个简单的题，发现个问题，不知道是因为oop的原因，还是random的原因，代码如下：
 class Coin
    {
        static void Main()
        {
            string exit = "0";
            while (exit != "1")
            {
                Coined c1 = new Coined();
                Coined c2 = new Coined();
                Coined c3 = new Coined();
                Coined c4 = new Coined();
                Coined c5 = new Coined();                c1.Flip();
                c2.Flip();
                c3.Flip();
                c5.Flip();
                c4.Flip();                Console.Write(c1.getFace() + "\t");
                Console.Write(c2.getFace() + "\t");
                Console.Write(c3.getFace() + "\t");
                Console.Write(c4.getFace() + "\t");
                Console.Write(c5.getFace() + "\t");
                Console.WriteLine();                Console.Write(c1.strValue() + "\t");
                Console.Write(c2.strValue() + "\t");
                Console.Write(c3.strValue() + "\t");
                Console.Write(c4.strValue() + "\t");
                Console.Write(c5.strValue() + "\t");
                Console.WriteLine();                int value = c1.Value() + c2.Value() + c3.Value();
                Console.WriteLine(value);
                Console.WriteLine();                exit = Console.ReadLine();
                Console.WriteLine();
            }
        }
    }    class Coined
    {
        Random r = new Random(DateTime.Now.Millisecond);
        private int face = 0;
        private int[] value = new int[] { 10, 20, 50, 100 };
        private int sValue = 0;
        public void Flip()
        {
            face = r.Next(2);
            
        }        public int getFace()
        {
            return face;
        }        public string strValue()
        {
            string s = "";
            s = face == 0 ? "Heads" : "Tails";
            return s;
        }        public int Value()
        {
            if (face != 0)
            {
                int i = r.Next(3);
                sValue = value[i];
            }
            return sValue;
        }
    }不知道为什么出来的结果都是5个都是一样的，找了好久也没有找到。希望大家指点一下，谢谢。还有Random r = new Random(DateTime.Now.Millisecond)和Random r = new Random(）有什么不一样的地方？