(S (S (S (BASENP (NN Six) (NNS people)) (VP (VBP have) (VP (VBN been) (VP (VBN killed))))) (SBAR (IN after) (S (NP (BASENP (DT a) (NN bus)) (VP (VBG carrying) (BASENP (JJ Polish) (NNS tourists)))) (VP (VBD crashed) (PP (IN in) (BASENP (NNP Serbia))))))) (PERIOD .))