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 Revolution makes a fragment. While Professor Koopman explained ... is a subordinate clause, which cannot stand alone as a complete sentence.
You might want to review the rules.