( Coal ( , ( ( as ( ( an ( excellent source ) ) ( of energy ) ) ) . ) ) )
(ROOT (FRAG (NP (NN Coal)) (, ,) (PP (IN as) (NP (NP (DT an) (JJ excellent) (NN source)) (PP (IN of) (NP (NN energy))))) (. .)))
Coal, as an excellent source of energy.
(ROOT (S (S (NP (NNP Coal)) (VP (VBZ is) (ADJP (JJ nonrenewable)))) (, ,) (CC and) (S (NP (DT the) (NN sun)) (VP (VBZ is) (ADJP (JJ renewable) (SBAR (S (VP (VBZ is) (SBAR (WHADVP (WRB how)) (S (NP (NP (NN coal)) (CC and) (NP (DT the) (NN sun))) (VP (VBP compare) (PP (IN as) (NP (NP (NNS sources)) (PP (IN of) (NP (NN energy)))))))))))))) (. .)))