(S (S (S (BASENP (NNS Insurgents)) (VP (VBD shot) (PP (IN at) (BASENP (DT the) (NNS troops))))) (CC and) (S (BASENP (PRP they)) (VP (VP (VBD returned) (BASENP (NN fire))) (COMMA ,) (S (VP (VBG killing) (BASENP (NN six))))))) (PERIOD .))