function show_answer (id, count) {
  // hide
  for (var index = 1; index <= count; index++) {
    document.getElementById('question-' + index).className = '';
    document.getElementById('answer-' + index).style.display = 'none';
  }

  // show
  document.getElementById('question-' + id).className = 'selected';
  document.getElementById('answer-' + id).style.display = 'inline';
}