Add these closing tags in the right order.

<html>
<body>
Marathon Results
<ol>
  <li>Winners
    <ul>
    <li>Weiss, Michael</li>
    <li>Tutukin, Ivan</li>
    <li>Potts, Andrew</li>
   </ul>
  </li>
</ol>
</body>
</html>]]>

Add </li> and then </ul>. Then add </li> to close the nested list and </ol> to close the ordered one.