Take a look at the item again:
While Professor Koopman explained the consequences of the French
Revolution, (A)
Tiffany and Faith sniffled uncomfortably in their
seats, (B)
suffocated by the cheap shaving lotion
(C) that Henry always
wore.
You wanted to do this:
While Professor Koopman explained the consequences of the French Revolution,
Tiffany and Faith sniffled uncomfortably in their
seats. Suffocated by the cheap shaving lotion
that Henry always wore.
A period after seats makes a fragment. Suffocated by the cheap shaving lotion is a past participle phrase and cannot stand alone as a complete sentence.
You might want to review the rules.
Go back to the sentence to try again.