“Why did the biology students almost fail?”/“They were bio-D-grade-able.”

A biology class pun is:
 
Q: Why did the biology students almost fail?
A: They were bio-D-grade-able.
 
“You’re not biodegradable, but you are bio-D-grade-able!”  was cited on Twitter on February 4, 2011. “What do biology students do when they do poorly on a test? They bio-D-grade” was posted on Reddit on July 7, 2016.
 
       
Twitter 
im a yucky man
‏@Mornacale
“You’re not biodegradable, but you are bio-D-grade-able!” #insultsCaptainPlanetshouldhaveused
1:04 PM - 4 Feb 2011
 
Twitter
Kim
‏@pumpkim_
My dad: if you were still in biology and you got a d, it would be bio-d-grade-able!! 😒
7:46 PM - 6 Dec 2013
 
Twitter
Meer-oku
‏@meerkthemeerkat
Why did I nearly fail my biology class?
Because I’m Bio “D” grade-able.
5:44 PM - 3 Feb 2015
 
Twitter
yikes
‏@nakedgusbutt
I’m bio D-grade able. Get it? Because i have a D in biology.
11:13 AM - 4 Apr 2015
 
reddit
What do biology students do when they do poorly on a test?
submitted July 7, 2016 by chameleoncookie
They bio-D-grade.