How can I preselect a radio button using javascript or jquery?
<p>I know this is probably easy, but I just can't figure it out.</p>

<p>I am working with a SAAS shopping cart solution so I can't adjust the form code or use PHP, so I need to use javascript or jquery.  </p>

<p>In this cart, I have a form....  </p>

<pre><code>&lt;form method="post" action="cart.php" id="productDetailsAddToCartForm"&gt;  
Please Select a Bottle Size:  
&lt;ul&gt;  
&lt;li&gt;&lt;label&gt;&lt;input name="variation[1]" type="radio" class="RadioButton" value="30"  /&gt; 11oz&lt;/label&gt;&lt;/li&gt; 
&lt;li&gt;&lt;label&gt;&lt;input name="variation[1]" type="radio" class="RadioButton" value="31"  /&gt; 33oz &lt;/label&gt;  
&lt;/li&gt;  
&lt;/ul&gt;  
&lt;/form&gt;
</code></pre>

<p>And I need to preselect the first radio button using jquery or javascript.  </p>

<p>Can you help?</p>
