Take a look at the item again:
Darryl has the messiest book bag (A)
of anyone Rachel knows; (B)
he essentially has a compost pile rotting in the main
compartment. (C)
For instance, pistachio shells, pencil shavings, and a brown banana.
You wanted to do this:
Darryl has the messiest book bag of anyone Rachel
knows, he essentially has a compost pile
rotting in the main compartment. For instance, pistachio shells, pencil
shavings, and a brown banana.
Changing the semicolon to a comma is a mistake. You have two main clauses at this juncture, and a comma is too wimpy a punctuation mark to connect them. There is a fragment. Look more closely!
You might want to review the rules.
Go back to the sentence to try again.