( ( When ( we ( burn coal ) ) ) ( we ( ( are ( ( ( reusing ( that ( ancient sun-energy ) ) ) , ) ( because ( coal ( is ( made ( from ( prehistoric trees ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (PRP we)) (VP (VBP burn) (NP (NN coal))))) (NP (PRP we)) (VP (VBP are) (VP (VBG reusing) (NP (DT that) (JJ ancient) (NN sun-energy)) (, ,) (SBAR (IN because) (S (NP (NN coal)) (VP (VBZ is) (VP (VBN made) (PP (IN from) (NP (JJ prehistoric) (NNS trees))))))))) (. .)))
When we burn coal we are reusing that ancient sun-energy, because coal is made from prehistoric trees.
(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)))))))))))))) (. .)))