( ( The ( ( sympathetic nervous ) system ) ) ( ( plays ( a ( secondary role ) ) ) . ) )
(ROOT (S (NP (DT The) (ADJP (JJ sympathetic) (JJ nervous)) (NN system)) (VP (VBZ plays) (NP (DT a) (JJ secondary) (NN role))) (. .)))
The sympathetic nervous system plays a secondary role.
(ROOT (S (NP (DT The) (JJ nervous) (NN system)) (VP (VBZ plays) (NP (NP (DT a) (JJ critical) (NN role)) (PP (IN in) (NP (NP (DT the) (NN regulation)) (PP (IN of) (NP (NN vascular) (NNS homeostasis))))))) (. .)))