Minor fix:
function qsa(str){return document.querySelectorAll(str)}
qsa('form[name=quiz_form]')[0].setAttribute('onsubmit','true');
window.setTimeout(fill,1000)
function fill(){
var a=qsa('form[name=quiz_form] input')
for(var i=0;i<a.length;i++){
if (a
[i].type=="checkbox" && Math.random()<0.5 )a
[i].click()
if(a
[i].type=="radio" && Math.random()<0.1)a
[i].click()} //<--
var c=qsa('form[name=quiz_form]')
c[0].submit()
}