title: find names of classes with the highest enrollement
body: <p>I have the following relation in database</p>
  
  <pre><code>ENROLLMENT (snum: int, cname:varchar(100))
  </code></pre>
  
  <p>where snum is the student id and cname is the course name</p>
  
  <p>and I want to find the name(s) of the class(s) with the most students enrolled.</p>