<p>"Restrictions</p>
<p>You may repeat the same course only once.
You may receive units for a repeated course only once.
You will not receive credit for a course repeated after you have completed a more advanced course in a true sequence with a passing grade (i.e., Math, Chemistry, or foreign languages)."</p>
<p>Source: [Repeating</a> Coursework](<a href=“http://collegecounseling.ucla.edu/repeat.html]Repeating”>http://collegecounseling.ucla.edu/repeat.html)</p>
<p>So no, you can’t retake after 31B, but further more, 31B requires 31A with a C- or better to begin with.</p>