( ( In ( the lungs ) ) ( ( the blood ) ( ( is ( ( supplied ( with oxygen ) ) ( before ( it ( ( ( returns ( to ( the heart ) ) ) , ) ( entering ( the ( left atrium ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (PP (IN In) (NP (DT the) (NNS lungs))) (NP (DT the) (NN blood)) (VP (VBZ is) (VP (VBN supplied) (PP (IN with) (NP (NN oxygen))) (SBAR (IN before) (S (NP (PRP it)) (VP (VBZ returns) (PP (TO to) (NP (DT the) (NN heart))) (, ,) (S (VP (VBG entering) (NP (DT the) (JJ left) (NN atrium))))))))) (. .)))
In the lungs the blood is supplied with oxygen before it returns to the heart, entering 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)))) (. .)))