( ( A ( familiar example ) ) ( ( ( ( is ( ( ( ( H 2 ) O ) -- ) ( ( ( two ( hydrogen atoms ) ) and ) ( one ( oxygen ( atom combine ) ) ) ) ) ) , ) ( forming ( a ( water molecule ) ) ) ) . ) )
(ROOT (S (NP (DT A) (JJ familiar) (NN example)) (VP (VBZ is) (NP (NP (NP (NNP H) (CD 2)) (NP (NNP O))) (: --) (NP (NP (CD two) (NN hydrogen) (NNS atoms)) (CC and) (NP (CD one) (NN oxygen) (NN atom) (NNS combine)))) (, ,) (S (VP (VBG forming) (NP (DT a) (NN water) (NN molecule))))) (. .)))
A familiar example is H 2 O--two hydrogen atoms and one oxygen atom combine, forming a water molecule.
(ROOT (S (NP (CD Two) (NN water) (NNS molecules)) (VP (VBP contain) (NP (NP (CD 4) (NN hydrogen) (NNS atoms)) (CC and) (NP (CD 2) (NN oxygen) (NNS atoms)))) (. .)))