Hi,
I am looking to build a simple calculating quiz using javascript and HTML. But I have hit a snag. I can't seem to get the buttons to do as I want. I make it to question 4, and then I can't select beyond it or else it changes and erasers the last selected question. Help!

Here is my code:
<!doctype html>
<html>
<head>
<meta charset="UTF-8">
<title>Quiz</title>

<style type="text/css">
<!--
.bgclr {background-color: white; color: black; font-weight: bold;}
-->
</style>

<script language="JavaScript">


<!-- Begin
// Insert number of questions
var numQues = 10;

// Insert number of choices in each question
var numChoi = 4;

// Insert number of questions displayed in answer area
var answers = new Array(10);

// Insert answers to questions
answers[0] = "All of the Above";
answers[1] = "";
answers[2] = "An enemy insect";
answers[3] = "Ash";
answers[4] = "Asia";
answers[5] = "Wood";
answers[6] = "A non for profit organization that Keeps Indiana Beautiful";
answers[7] = "Green";
answers[8] = "Ashley";
answers[9] = "All of the Above";

function getScore(form) {
var score = 0;
var currElt;
var currSelection;
for (i=0; i<numQues; i++) {
currElt = i*numChoi;
for (j=0; j<numChoi; j++) {
currSelection = form.elements[currElt + j];
if (currSelection.checked) {
if (currSelection.value == answers[i]) {
score++;
break;
}
}
}
}
score = Math.round(score/numQues*100);
form.percentage.value = score + "%";
var correctAnswers = "";
for (i=1; i<=numQues; i++) {
correctAnswers += i + ". " + answers[i-1] + "\r\n";
}
form.solutions.value = correctAnswers;
}

</script>
</head>


<body>
<h3>Web Design Quiz</h3>

<form name="quiz">
1. Why do we need trees?
<ul style="margin-top: 1pt">
<li><input type="radio" name="q1" value="Shade">Shade</li>
<li><input type="radio" name="q1" value="Oxygen">Oxygen</li>
<li><input type="radio" name="q1" value="Animal Habitats">Animal Habitats</li>
<li><input type="radio" name="q1" value="All of the Above">All of the Above</li>
</ul>

2. Which if these is an ash tree?
<ul style="margin-top: 1pt">

</ul>
3. What is an Emerald Ash Borer?
<ul style="margin-top: 1pt">
<li><input type="radio" name="q3" value="Midwestern Species of Bird">Midwestern Species of Bird</li>
<li><input type="radio" name="q3" value="A mineral">A mineral</li>
<li><input type="radio" name="q3" value="An enemy insect">An enemy insect</li>
<li><input type="radio" name="q3" value="A super hero">A super hero</li>
</ul>
4. What type of tree is the Emerald Ash Borer found in?
<ul style="margin-top: 1pt">
<li><input type="radio" name="q4" value="Ash">Ash</li>
<li><input type="radio" name="q4" value="Maple">Maple</li>
<li><input type="radio" name="q4" value="Oak">Oak</li>
<li><input type="radio" name="q4" value="Pine">Pine</li>
</ul>
5. Where did Emerald Ash Borers come from?
<ul style="margin-top: 1pt">
<li><input type="radio" name="q4" value="Asia">Asia</li>
<li><input type="radio" name="q4" value="Africa">Africa</li>
<li><input type="radio" name="q4" value="South America">South America</li>
<li><input type="radio" name="q4" value="North America">North America</li>
</ul>
6. What do the larva feed on?
<ul style="margin-top: 1pt">
<li><input type="radio" name="q4" value="Leaves">Leaves</li>
<li><input type="radio" name="q4" value="McDonalds">McDonalds</li>
<li><input type="radio" name="q4" value="Wood">Wood</li>
<li><input type="radio" name="q4" value="Dirt">Dirt</li>
</ul>
7. What is KIB?
<ul style="margin-top: 1pt">
<li><input type="radio" name="q4" value="Kibbles In Bits">Kibbles In Bits</li>
<li><input type="radio" name="q4" value="A non for profit organization that Keeps Indiana Beautiful">A non for profit organization that Keeps Indiana Beautiful</li>
<li><input type="radio" name="q4" value="A tree">A tree</li>
<li><input type="radio" name="q4" value="An insect">An insect</li>
</ul>
8. What color is the Merald Ash Borer
<ul style="margin-top: 1pt">
<li><input type="radio" name="q4" value="Red">Red</li>
<li><input type="radio" name="q4" value="Green">Green</li>
<li><input type="radio" name="q4" value="Orange">Orange</li>
<li><input type="radio" name="q4" value="Purple">Purple</li>
</ul>
9. What is the name of the woman in the video?
<ul style="margin-top: 1pt">
<li><input type="radio" name="q4" value="Brandy">Brandy</li>
<li><input type="radio" name="q4" value="Tom">Tom</li>
<li><input type="radio" name="q4" value="Ashley">Ashley</li>
<li><input type="radio" name="q4" value="Colleen">Colleen</li>
</ul>
10. What can you do to help?
<ul style="margin-top: 1pt">
<li><input type="radio" name="q4" value="Volunteer with KIB">Volunteer with KIB</li>
<li><input type="radio" name="q4" value="Don't transport wood to other locations">Don't transport wood to other locations</li>
<li><input type="radio" name="q4" value="Be educated and spread awareness">Be educated and spread awareness</li>
<li><input type="radio" name="q4" value="All of the Above">All of the Above</li>
</ul>

<input type="button" value="Get score" onClick="getScore(this.form)">
<input type="reset" value="Clear answers">
<p> Score = <strong><input class="bgclr" type="text" size="5" name="percentage" disabled></strong><br><br>
Correct answers:<br>
<textarea class="bgclr" name="solutions" wrap="virtual" rows="4" cols="30" disabled>
</textarea>
</form>
</body>
</html>

Thanks so much, anything to help would be awesome.