Here is the original item:
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 participle phrase, which cannot stand alone as a complete sentence.
You might want to review the rules.