function checkanswers(button, parent)
{
    button.disabled = true;
    button.style.display = 'none';
    var sheet=document.getElementById(parent);
    var aSpans = document.getElementsByTagName("span");
    var count = 0;
    var score = 0;
    for (var iSpan = 0; iSpan < aSpans.length; iSpan++) {
        var oSpan = aSpans[iSpan];
        if (oSpan.className == 'S' + parent + 'Q')
        {
          var aSelects = oSpan.getElementsByTagName("select");
          var aExplains = oSpan.getElementsByTagName("span");
          for (var iSelect = 0; iSelect < aSelects.length; iSelect++) {
            if (aSelects[iSelect].className = "Q") {
                count++;
                var sel = aSelects[iSelect];
                var opt = sel.options;
                var answer = "";
                var useranswer = opt[sel.selectedIndex].text;
                var explain = "";
                //collect answer
                for (var i = 0; i < opt.length; i++)
                {
                    if (opt[i].value == "$$") {
                        answer = opt[i].text;
                        break;
                    }
                } 
                for (var iExplain = 0; iExplain < aExplains.length; iExplain++) {
                    if (aExplains[iExplain].className = "exp") {
                        explain = '<font color=gray><i>(' + aExplains[iExplain].innerHTML + ')</i></font>';
                    }
                }
                if (answer==useranswer) {
                    score++;
                    oSpan.innerHTML = ' <font color=blue>' + answer + '</font> ';
                }
                else {
                    if (sel.selectedIndex == 0) {
                        oSpan.innerHTML = ' <i><font color=blue>' + answer + '</font></i> ' + explain;
                    } else {
                        oSpan.innerHTML = ' <font color=red><strike>' + useranswer + '</strike></font> <i><font color=blue>' + answer + '</font></i> ' + explain;
                    }
                }
            }
          }
        }
    }
    var answer = document.getElementById(parent + 'Results');
    answer.innerHTML = "You scored " + score + " out of " + count;
}