( ( ( the fusion ) ( of two ) ) ( ( protons ( into ( a ( helium nucleus ) ) ) ) . ) )
(ROOT (S (NP (NP (DT the) (NN fusion)) (PP (IN of) (NP (CD two)))) (VP (VBZ protons) (PP (IN into) (NP (DT a) (NNP helium) (NN nucleus)))) (. .)))
the fusion of two protons into a helium nucleus.
(ROOT (S (PP (IN In) (NP (DT the) (JJ nuclear) (NN fusion) (NN process))) (, ,) (NP (CD two) (JJ light) (NNS nuclei)) (VP (VBP combine) (S (VP (TO to) (VP (VB produce) (NP (NP (DT a) (JJR heavier) (NN nucleus)) (CC and) (NP (JJ great) (NN energy))))))) (. .)))