Take another look at the item:

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.

Adding a comma after bag creates an error. Of anyone is a prepositional phrase. When you connect a phrase of this type to the end of a main clause, you need no punctuation.

You might want to review the rules.

Go back to the sentence to try again.

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