Which sentence is written incorrectly?
A) The two students who started a fight at the pep rally, both sophomores, were removed from the gymnasium.
B) The committee looked at two solutions for the sudden drop in tax revenue-- both of which, were valid.
C) Although I'm not usually scared of dogs, I have to admit that seeing a Great Dane without a leash in my yard made me pause.
D) Sophie wanted to show off both her new instamatic camera and her brand-new, super-expensive, purple shoes.