title: Access tag "option" in HtmlElement
body: <p>need to change this:</p>
  
  <pre><code>&lt;select name="asdf"&gt;
      &lt;option selected&gt;a&lt;/option&gt;
      &lt;option&gt;b&lt;/option&gt;
      &lt;option&gt;c&lt;/option&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p>I got the <code>HtmlElement</code> but cant change it via <code>htmlEle.SetAttribute("value", "c");</code></p>
  
  <p>I want to change the selected option from <strong>a</strong> to <strong>c</strong>.</p>