Energy-related activities are the primary source of U.S. man-made greenhouse gas emissions.
( ( Energy-related activities ) ( ( are ( ( the ( primary source ) ) ( of ( U.S. ( man-made ( greenhouse ( gas emissions ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Energy-related) (NNS activities)) (VP (VBP are) (NP (NP (DT the) (JJ primary) (NN source)) (PP (IN of) (NP (NNP U.S.) (NNP man-made) (NN greenhouse) (NN gas) (NNS emissions))))) (. .)))
Producing energy is the main source of US greenhouse gas emissions.
( ( Producing energy ) ( ( is ( ( the ( main source ) ) ( of ( US ( greenhouse ( gas emissions ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Producing) (NN energy)) (VP (VBZ is) (NP (NP (DT the) (JJ main) (NN source)) (PP (IN of) (NP (NNP US) (NN greenhouse) (NN gas) (NNS emissions))))) (. .)))