( D ( -RRB- ( Water ( ( is ( formed ( from ( ( ( 2 ( hydrogen atoms ) ) and ) ( 1 ( oxygen atom ) ) ) ) ) ) . ) ) ) )
(ROOT (S (LST (JJ D)) (-RRB- -RRB-) (NP (VBG Water)) (VP (VBZ is) (VP (VBN formed) (PP (IN from) (NP (NP (CD 2) (NN hydrogen) (NNS atoms)) (CC and) (NP (CD 1) (NN oxygen) (NN atom)))))) (. .)))
D) Water is formed from 2 hydrogen atoms and 1 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.