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 cars is the main source of US greenhouse gas emissions.
( ( Producing cars ) ( ( is ( ( the ( main source ) ) ( of ( US ( greenhouse ( gas emissions ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Producing) (NNS cars)) (VP (VBZ is) (NP (NP (DT the) (JJ main) (NN source)) (PP (IN of) (NP (NNP US) (NN greenhouse) (NN gas) (NNS emissions))))) (. .)))