You know you're a 3L when...
You've done all of the reading for the first few weeks of non-profits class. But you still haven't figured out that "tax-exempt" for 501(c)3 organizations means exempt only from corporate income tax (and tax-deductible in some cases via the operation of 170, but I digress).
A good way to make sure that you, the professor, and all of the other students are convinced of your inability to concentrate on school this year is to raise your hand and ask about the importance of the employment tax exemption in the context of the problem the professor would like to move beyond.
Oh. There's no such thing as an employment tax exemption for 501(c)3 orgs. Tax exempt doesn't mean completely tax exempt. The professor knows this. The professor's response to your question will make it clear that the book has explained this. Your classmates' embarrassed silence will show that they, too, knew it.
And the great thing about 3L is... you'll laugh at yourself. Out loud.