function change_answer(i)
{
  if (document.getElementById('id-answer-'+i).className == 'row_hidden')
    show_answer(i);
  else
    hide_answer(i);
  return false;
}

function show_answer(i)
{
  document.getElementById('id-answer-'+i).className = 'row_visible';
  return false;
}

function hide_answer(i)
{
  document.getElementById('id-answer-'+i).className = 'row_hidden';
  return false;
}