( ( is ( burned ( to ( produce ( ( heat and ) electricity ) ) ) ) ) . )
(ROOT (S (VP (VBZ is) (VP (VBN burned) (S (VP (TO to) (VP (VB produce) (NP (NN heat) (CC and) (NN electricity))))))) (. .)))
is burned to produce heat and electricity.
(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.