( ( ( Oxygen-rich blood ) ( from ( the lungs ) ) ) ( ( enters ( the ( left atrium ) ) ) . ) )
(ROOT (S (NP (NP (JJ Oxygen-rich) (NN blood)) (PP (IN from) (NP (DT the) (NNS lungs)))) (VP (VBZ enters) (NP (DT the) (JJ left) (NN atrium))) (. .)))
Oxygen-rich blood from the lungs enters the left atrium.
(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)))) (. .)))