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