( ( The ( only disadvantage ) ) ( ( is ( that ( ( oxygen ( in ( the fuel ) ) ) ( ( can not ) ( contribute energy ) ) ) ) ) ; ) )
(ROOT (S (NP (DT The) (JJ only) (NN disadvantage)) (VP (VBZ is) (SBAR (IN that) (S (NP (NP (NN oxygen)) (PP (IN in) (NP (DT the) (NN fuel)))) (VP (MD can) (RB not) (VP (VB contribute) (NP (NN energy))))))) (: ;)))
The only disadvantage is that oxygen in the fuel cannot contribute energy;
(ROOT (S (NP (NNS Plants)) (VP (CONJP (RB not) (JJ only)) (VP (VBP contribute) (NP (NN food))) (CC but) (VP (VBD oxygen) (PP (IN for) (NP (NNS organisms))))) (. .)))