(S (S (BASENP (PRP He)) (VP (VBZ estimates) (SBAR (IN that) (S (NP (BASENP (RB nearly) (NN two-thirds)) (PP (IN of) (NP (BASENP (DT the) (NN 278,000) (JJ yearly) (NNS flights)) (PP (IN between) (BASENP (JJ Canadian) (NNS cities)))))) (VP (VBP cross) (PP (IN over) (BASENP (DT the) (NNP U.S.) (NN border)))))))) (PERIOD .))