Sometimes It Is Difficult to Decide Whether Something Your Professor

Sometimes it is difficult to decide whether something your professor said should go into your notes. What advice does the text give about dealing with such uncertainty?

A) If it is not related to the main topic, forget it.
B) Put absolutely every word the professor says in your notes, and you will never go wrong.
C) Look around the room to see if other students are writing it down.
D) If you aren't sure, write it in your notes.