( They ( usually ( ( ( reproduce sexually ) ( with ( internal fertilization ) ) ) . ) ) )
(ROOT (S (NP (PRP They)) (ADVP (RB usually)) (VP (VB reproduce) (ADVP (RB sexually)) (PP (IN with) (NP (JJ internal) (NN fertilization)))) (. .)))
They usually reproduce sexually with internal fertilization.
(ROOT (S (NP (NNS Amphibians)) (ADVP (RB sexually)) (VP (VB reproduce) (PP (IN through) (NP (JJ external) (CC or) (JJ internal) (NN fertilization)))) (. .)))