( ( Water molecules ) ( each ( ( contain ( ( ( two ( hydrogen atoms ) ) and ) ( one ( oxygen atom ) ) ) ) . ) ) )
(ROOT (S (NP (NNP Water) (NNS molecules)) (DT each) (VP (VBP contain) (NP (NP (CD two) (NN hydrogen) (NNS atoms)) (CC and) (NP (CD one) (NN oxygen) (NN atom)))) (. .)))
Water molecules each contain two hydrogen atoms and one oxygen atom.
(ROOT (S (NP (NP (CD 2) (NN hydrogen)) (, ,) (NP (CD 1) (NN oxygen) (NNS atoms))) (VP (VBP combine) (S (VP (TO to) (VP (VB make) (PRT (RP up)) (NP (NP (DT a) (NN molecule)) (PP (IN of) (NP (NN water)))))))) (. .)))
2 hydrogen, 1 oxygen atoms combine to make up a molecule of water.