var cur;
function showanswer(qid) {
  qid = "q" + qid;
  if (cur) document.getElementById(cur).style.display = "none";
  if (cur != qid) {
    document.getElementById(qid).style.display = "block";
    cur = qid;
  } else {
    cur = null;
  }
  return false;
}