(S (S (PP (IN On) (BASENP (NNP Monday))) (COMMA ,) (S (BASENP (NN city) (NNS officials)) (VP (VP (VBD gave) (BASENP (DT the) (NN cause))) (PP (IN as) (NP (BASENP (JJ combustible) (NN dust)) (PP (IN in) (NP (BASENP (DT the) (NN air)) (PP (IN at) (BASENP (DT a) (NN polishing) (NN workshop)))))))))) (PERIOD .))