(S (S (BASENP (PRP It)) (VP (VBZ is) (VP (VBN thought) (SBAR (IN that) (S (S (BASENP (DT the) (NN fire)) (VP (VBD began))) (SBAR (WHADVP (WRB when)) (S (NP (BASENP (NNS workers)) (PP (IN in) (BASENP (NNP Agua) (NNP Dulce)))) (VP (VP (VBD caused) (BASENP (NNS sparks))) (PP (IN by) (S (VP (VBG hammering) (BASENP (DT the) (NNS bolts))) (SBAR (WHADVP (WRB when)) (S (BASENP (PRP they)) (VP (VBD were) (VP (VP (VBG removing) (BASENP (DT a) (NN tire))) (PP (IN from) (BASENP (DT a) (NN rim))))))))))))))))) (PERIOD .))