( ( The brain ) ( ( is ( ( the ( ( most complex ) organ ) ) ( in ( ( a ( vertebrate 's ) ) body ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN brain)) (VP (VBZ is) (NP (NP (DT the) (ADJP (RBS most) (JJ complex)) (NN organ)) (PP (IN in) (NP (NP (DT a) (NN vertebrate) (POS 's)) (NN body))))) (. .)))
The brain is the most complex organ in a vertebrate's body.
(ROOT (S (NP (DT The) (NN brain)) (VP (VBZ is) (NP (NP (DT the) (ADJP (RBS most) (JJ complex)) (NN organ)) (PP (IN in) (NP (DT the) (JJ human) (NN body))))) (. .)))