(S (S (BASENP (DT The) (NNS workers)) (VP (MD may) (VP (VB have) (VP (VBN died) (PP (IN from) (NP (NP (NP (NP (BASENP (JJ poisonous) (NNS gasses)) (COMMA ,) (BASENP (NN smoke) (NN inhalation))) (COMMA ,) (BASENP (NNP suffocation))) (COMMA ,) (BASENP (NNS cave-ins))) (CC or) (BASENP (NN carbon) (NN monoxide) (NN poisoning)))))))) (PERIOD .))