( Blood ( ( flows ( from ( ( ( the lungs ) , ) ( where ( it ( ( picks up ) ( ( oxygen ( , ( ( through ( the ( pulmonary veins ) ) ) , ) ) ) ( to ( ( the ( left atrium ) ) ( of ( the heart ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Blood)) (VP (VBZ flows) (PP (IN from) (NP (NP (DT the) (NNS lungs)) (, ,) (SBAR (WHADVP (WRB where)) (S (NP (PRP it)) (VP (VBZ picks) (PRT (RP up)) (NP (NP (NP (NN oxygen)) (PRN (, ,) (PP (IN through) (NP (DT the) (JJ pulmonary) (NNS veins))) (, ,))) (PP (TO to) (NP (NP (DT the) (JJ left) (NN atrium)) (PP (IN of) (NP (DT the) (NN heart)))))))))))) (. .)))
Blood flows from the lungs, where it picks up oxygen, through the pulmonary veins, to the left atrium of the heart.
(ROOT (S (NP (NP (NNP Blood)) (PP (IN from) (NP (DT the) (NNS lungs)))) (VP (VBZ enters) (PP (IN into) (NP (DT the) (JJ left) (NN atrium)))) (. .)))