my solution

[Test]
        public void TestExercise4()
        {
            Programmeren2Tests.Chapter12Test.TestExercise4(Exercise4);
        }

        public static int Exercise4()
        {
            int count = 0;
            foreach (string str in LoadAliceInWonderland())
                if (str == "queen")
                    count++;
            return count;
            //throw new NotImplementedException();
        }

        //load the book (from file) and return it as a string array
        public static string[] LoadAliceInWonderland()
        {
            string aliceFile = Path.Combine(Environment.CurrentDirectory, "bestanden\\alice_in_wonderland.txt");
            string text = File.ReadAllText(aliceFile).ToLower();
            string[] words = removeUselessValues(text).Split();
            return words;
        }

        public static string removeUselessValues(string s)
        {
            string result = "";
            foreach (char c in s)
                result += (c.Equals('q') || c.Equals('u') || c.Equals('e') || c.Equals('n')) ? c : ' ';
            return result;
        }