e.randi(8, 12);
  for(var i=0;i<n;i++) {
    sel.append('option').html(ITEMS[i]);
  }

  var expected = [];
  var gt_txt = '';
  while(expected.length < MAX_CHOSEN){
    var ix = core.randi(0, n); // ground truth index
    if(expected.indexOf(ITEMS[ix]) !== -1) continue;
    expected.push(ITEMS[ix]);
    if (expected.length > 1)  gt_txt += ', '
    gt_txt += ITEMS[ix];
    if(core.sample([true, false]) === true) break;
  }

  return {gt_txt: gt_txt, expected: expected};
}

var bindSubmit = function(div, scr