(S (S (S (BASENP (DT The) (NN leak)) (VP (VBD was) (VP (VBN created)))) (SBAR (WHADVP (WRB when)) (S (BASENP (DT the) (NN train)) (VP (VBD struck) (NP (BASENP (DT a) (NN concrete) (NN block)) (SBAR (WDT that) (S (BASENP (NNS vandals)) (VP (VBD left) (PP (IN on) (BASENP (DT the) (NNS tracks))))))))))) (PERIOD .))