margin-left:'+core.randi(0,20)+'px;';
  s += 'margin-top:'+core.randi(0,20)+'px;';
  d3.select('#form').attr('style', s);

  // and submit button a bit too
  d3.select('#subbtn').attr('style', 'margin-top:'+core.randi(0,20)+'px;');
}

var genProblem = function() {
  var div = d3.select('#area');
  div.html('');

  // click-option
  div.append('div').attr('id', 'boxes')
  var div_option = d3.select('#boxes');
  div_option.html('');
  var correctElement = createElements(div_option);

  // enter-text
  div.app