(S (S (BASENP (DT The) (NNP EC)) (VP (VBD required) (S (BASENP (NNP IAG)) (VP (TO to) (VP (VB surrender) (NP (NP (BASENP (DT a) (NN number)) (PP (IN of) (BASENP (NN flight) (NNS slots)))) (PP (IN at) (BASENP (DT the) (NN airport))))))))) (PERIOD .))