( ( As ( coal burns ) ) ( , ( ( ( sulfur gases ) ( from ( the coal ) ) ) ( ( ( combine ( with limestone ) ) ( to ( form ( ( a ( solid compound ) ) ( that ( is ( recovered ( with ash ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN As) (NP (NN coal) (NNS burns))) (, ,) (NP (NP (NN sulfur) (NNS gases)) (PP (IN from) (NP (DT the) (NN coal)))) (VP (VBP combine) (PP (IN with) (NP (NN limestone))) (S (VP (TO to) (VP (VB form) (NP (NP (DT a) (JJ solid) (NN compound)) (SBAR (WHNP (WDT that)) (S (VP (VBZ is) (VP (VBN recovered) (PP (IN with) (ADJP (JJ ash)))))))))))) (. .)))
As coal burns, sulfur gases from the coal combine with limestone to form a solid compound that is recovered with ash.
(ROOT (S (NP (PRP We)) (VP (VBP call) (NP (NP (DT the) (JJ solid) (NN form)) (PP (IN of) (NP (JJ hydrocarbons) (NN coal))))) (. .)))