( ( A chemical ) ( mutagen . ) )
(ROOT (S (NP (DT A) (NN chemical)) (VP (VBP mutagen)) (. .)))
A chemical mutagen .
(ROOT (S (NP (NP (NNP Radiation)) (, ,) (NP (NNS chemicals)) (, ,) (CC and) (NP (JJ infectious) (NNS agents))) (VP (VBP are) (NP (NP (NNS types)) (PP (IN of) (NP (NNS mutagens))))) (. .)))