proves that not only blockbusters pollute the summer movie pool 
(ROOT (VP (VBZ proves) (SBAR (IN that) (S (NP (RB not) (RB only) (NNS blockbusters)) (VP (VBP pollute) (NP (DT the) (NN summer) (NN movie) (NN pool)))))))
(ROOT (VP (VBZ ) (SBAR (IN ) (S (NP (RB ) (RB ) (NNS )) (VP (VBP ) (NP (DT ) (NN ) (NN ) (NN )))))))