C#-Code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows;
using System.Windows.Controls;
using System.Xml.Linq;

namespace WPFQuiz
{
    /// <summary>
    /// Interaktionslogik für MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        static Random rnd = new Random();

        XDocument doc;
        List<Question> questions;
        Question currentQuestion;
        public MainWindow()
        {
            InitializeComponent();
            doc = XDocument.Load(@"Dateipfad");
            questions = (from q in doc.Descendants("Frage") select new Question() { Id = Convert.ToInt32(q.Attribute("Id").Value), CorrectAnswer = q.Attribute("Richtig").Value, Text = q.Attribute("Text").Value, AnswerA = q.Attribute("A").Value, AnswerB = q.Attribute("B").Value, AnswerC = q.Attribute("C").Value, AnswerD = q.Attribute("D").Value }).ToList();
            NextQuestion();
        }

        private void NextQuestion()
        {
            int index = rnd.Next(0, questions.Count);
            currentQuestion = questions[index];
            textBlockCount.Text = currentQuestion.Id.ToString();
            textBlockFrage.Text = currentQuestion.Text;
            buttonA.Content = currentQuestion.AnswerA;
            buttonB.Content = currentQuestion.AnswerB;
            buttonC.Content = currentQuestion.AnswerC;
            buttonD.Content = currentQuestion.AnswerD;
        }

        private void EnableAll(bool enabled)
        {
            buttonA.IsEnabled = enabled;
            buttonB.IsEnabled = enabled;
            buttonC.IsEnabled = enabled;
            buttonD.IsEnabled = enabled;
        }

        private void button_Click(object sender, RoutedEventArgs e)
        {
            EnableAll(false);
            string button = ((Button)sender).Name.Substring(6, 1);
            if (button == currentQuestion.CorrectAnswer)
            {
                MessageBox.Show("Richtig");
            }
            else
            { MessageBox.Show("Falsch! Richtig ist: " + currentQuestion.CorrectAnswer); }
        }

        private void buttonNext_Click(object sender, RoutedEventArgs e)
        {
            EnableAll(true);
            NextQuestion();
        }
    }

    class Question
    {
        public int Id { get; set; }
        public string CorrectAnswer { get; set; }
        public string Text { get; set; }
        public string AnswerA { get; set; }
        public string AnswerB { get; set; }
        public string AnswerC { get; set; }
        public string AnswerD { get; set; }
    }
}