( ( ( The ( only thing ) ) ( that ( ( ( holds ( the quarks ) ) together ) ( to ( make ( ( protons and ) neutrons ) ) ) ) ) ) ( ( is ( energy ( -LRB- ( ( carried ( by gluons ) ) -RRB- ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (JJ only) (NN thing)) (SBAR (WHNP (WDT that)) (S (VP (VBZ holds) (NP (DT the) (NNS quarks)) (ADVP (RB together)) (S (VP (TO to) (VP (VB make) (NP (NNS protons) (CC and) (NNS neutrons))))))))) (VP (VBZ is) (NP (NP (NN energy)) (PRN (-LRB- -LRB-) (VP (VBN carried) (PP (IN by) (NP (NNS gluons)))) (-RRB- -RRB-)))) (. .)))
The only thing that holds the quarks together to make protons and neutrons is energy ( carried by gluons ) .
(ROOT (S (NP (NP (DT The) (CD two) (JJ main) (JJ fundamental) (NNS particles)) (SBAR (WHNP (WDT that)) (S (VP (VBP make) (PRT (RP up)) (NP (NNS neutrons)))))) (VP (VBP are) (NP (NNS quarks) (CC and) (NNS gluons))) (. .)))