( ( ( ( ( Fuel cells ) , ) ( which ( ( are ( ( ( ( ( quieter , ) cleaner ) , ) and ) ( more efficient ) ) ) ( than ( conventional ( ( engines or ) turbines ) ) ) ) ) ) , ) ( ( ( ( ( ( convert ( hydrocarbons ( such ( as methane ) ) ) ) ( into ( carbon ( ( dioxide and ) hydrogen ) ) ) ) , ) and ) ( then ( ( ( combine ( the hydrogen ) ) ( with oxygen ) ) ( in ( ( the air ) ( in ( ( a ( catalytic reaction ) ) ( that ( produces electricity ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NN Fuel) (NNS cells)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBP are) (ADJP (ADJP (JJ quieter)) (, ,) (ADJP (JJR cleaner)) (, ,) (CC and) (ADJP (RBR more) (JJ efficient))) (PP (IN than) (NP (JJ conventional) (NNS engines) (CC or) (NNS turbines)))))) (, ,)) (VP (VP (VB convert) (NP (NP (NNS hydrocarbons)) (PP (JJ such) (IN as) (NP (NN methane)))) (PP (IN into) (NP (NN carbon) (NN dioxide) (CC and) (NN hydrogen)))) (, ,) (CC and) (VP (ADVP (RB then)) (VB combine) (NP (DT the) (NN hydrogen)) (PP (IN with) (NP (NN oxygen))) (PP (IN in) (NP (NP (DT the) (NN air)) (PP (IN in) (NP (NP (DT a) (JJ catalytic) (NN reaction)) (SBAR (WHNP (WDT that)) (S (VP (VBZ produces) (NP (NN electricity))))))))))) (. .)))
Fuel cells, which are quieter, cleaner, and more efficient than conventional engines or turbines, convert hydrocarbons such as methane into carbon dioxide and hydrogen, and then combine the hydrogen with oxygen in the air in a catalytic reaction that produces electricity.
(ROOT (S (NP (NNP Combustion) (NNS reactions)) (VP (VBP involve) (S (NP (NP (DT the) (NN reaction)) (PP (IN of) (NP (NP (DT a) (NN hydrocarbon)) (PP (IN with) (NP (NN oxygen) (NN gas)))))) (VP (TO to) (VP (VB produce) (NP (NN water) (CC and) (NN carbon) (NN dioxide)))))) (. .)))