( ( One ( of ( ( the ( human ( body systems ) ) ) ( they researched ) ) ) ) ( ( was ( the ( Circulatory System ) ) ) . ) )
(ROOT (S (NP (NP (CD One)) (PP (IN of) (NP (NP (DT the) (JJ human) (NN body) (NNS systems)) (SBAR (S (NP (PRP they)) (VP (VBN researched))))))) (VP (VBD was) (NP (DT the) (NNP Circulatory) (NNP System))) (. .)))
One of the human body systems they researched was the Circulatory System.
(ROOT (S (NP (NNS Hormones)) (ADVP (RB generally)) (VP (VBP travel) (PP (IN through) (NP (NP (DT the) (JJ circulatory) (NN system) (NN system)) (PP (IN of) (NP (DT the) (NN body)))))) (. .)))