function changeChoice(was) {
  this.was = was;
  var wort = document.getElementById('woerter').style;
  var unwort = document.getElementById('unwoerter').style;

  var wortli = document.getElementById('wli').style;
  var unwortli = document.getElementById('unwli').style;

  if (this.was == 'woerter') {
    wort.display = 'block';
    unwort.display = 'none';

    wortli.color = '#993333';
    unwortli.color = '#666666';
  } else {
    wort.display = 'none';
    unwort.display = 'block';

    wortli.color = '#666666';
    unwortli.color = '#993333';
  }
}