function show_question(id) {
  var cur_question = parseInt($('current_question').value);
          
  if (cur_question != 0) {
    hide_question(cur_question);
  }
  
  $('current_question').value = id;
  var new_question_img = 'question_' + id + '_image';

  $(new_question_img).src = 'images/icon_close.gif'; 
                                   
  var answer_id = 'answer_' + id;
  $(answer_id).show();
}

function hide_question(id) {
  var img_id = 'question_' + id + '_image';
  $(img_id).src = 'images/icon_open.gif'; 
  
  var a_id = 'answer_' + id; 
  $(a_id).hide();
}