( Disturbing ( ( can ( be ( done ( by ( ( internal ( or ( external methods ) ) ) ( -LRB- ( environmental -RRB- ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Disturbing)) (VP (MD can) (VP (VB be) (VP (VBN done) (PP (IN by) (NP (NP (JJ internal) (CC or) (JJ external) (NNS methods)) (PRN (-LRB- -LRB-) (NP (JJ environmental)) (-RRB- -RRB-))))))) (. .)))
Disturbing can be done by internal or external methods (environmental).
(ROOT (S (NP (NNS Amphibians)) (ADVP (RB sexually)) (VP (VB reproduce) (PP (IN through) (NP (JJ external) (CC or) (JJ internal) (NN fertilization)))) (. .)))