( Consider ( ( coal , ) ( ( the source ) ( of ( ( 56 % ) ( of ( ( the electricity ) ( generated ( in ( the U.S. ) ) ) ) ) ) ) ) ) )
(ROOT (S (VP (VB Consider) (NP (NP (NN coal)) (, ,) (NP (NP (DT the) (NN source)) (PP (IN of) (NP (NP (CD 56) (NN %)) (PP (IN of) (NP (NP (DT the) (NN electricity)) (VP (VBN generated) (PP (IN in) (NP (DT the) (NNP U.S.)))))))))))))
Consider coal, the source of 56% of the electricity generated in the U.S.
(ROOT (S (NP (NNP Coal)) (VP (VBZ is) (NP (NP (DT the) (NN source)) (PP (IN of) (NP (JJS most) (NN electricity))))) (. .)))