CLAS Question

<p>I was cruising through the website and I noticed a little known gem that you could not take a lower level class in a department for a CLAS requirement if you had taken a higher level one previously. In other words, if you have taken a 2000 level Astronomy course for 3 of the 6 hours of the physical science requirement, can you come back and take a 1000 level course for the remaining 3 hours? Am I reading this correctly? </p>