( Coal ( ( is ( ( ( mined and ) burned ) ( to ( produce ( heat energy ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Coal)) (VP (VBZ is) (VP (VBN mined) (CC and) (VBN burned) (S (VP (TO to) (VP (VB produce) (NP (NN heat) (NN energy))))))) (. .)))
Coal is mined and burned to produce heat energy.
(ROOT (S (NP (NNP Heat)) (VP (VBZ is) (VP (VBN produced) (SBAR (WHADVP (WRB when)) (S (NP (NN paper)) (VP (VBZ is) (VP (VBN burned))))))) (. .)))
Heat is produced when paper is burned.