( They ( generally ( ( only ( eat plants ) ) . ) ) )
(ROOT (S (NP (PRP They)) (ADVP (RB generally)) (VP (ADVP (RB only)) (VBP eat) (NP (NNS plants))) (. .)))
They generally only eat plants.
(ROOT (S (NP (DT The) (NN heterotroph)) (VP (VBZ eats) (NP (UCP (ADJP (JJ only)) (CC or) (ADVP (RB mainly))) (NNS plants))) (. .)))