(S (S (S (BASENP (DT The) (NNS helicopters)) (VP (VBP are) (VP (VBG being) (VP (VBN used) (S (VP (TO to) (VP (VB fight) (BASENP (DT the) (NNS fires))))))))) (SBAR (WHADVP (WRB where)) (S (BASENP (NN ground) (NNS crews)) (VP (VP (MD ca) (RB n't)) (VP (VB reach) (COMMA ,) (PP (IN such) (PP (IN as) (NP (BASENP (JJ steep) (NN mountain) (NNS passes)) (CC and) (BASENP (NNS valleys)))))))))) (PERIOD .))