( ( ( ( ( ( An element ) ( ( can not ) ( be ( ( broken down ) ( into ( simpler substances ) ) ) ) ) ) , ) but ) ( ( the ( unknown substance ) ) ( ( breaks down ) ( into ( ( ( a solid ) and ) ( a gas ) ) ) ) ) ) . )
(ROOT (S (S (NP (DT An) (NN element)) (VP (MD can) (RB not) (VP (VB be) (VP (VBN broken) (PRT (RP down)) (PP (IN into) (NP (JJR simpler) (NNS substances))))))) (, ,) (CC but) (S (NP (DT the) (JJ unknown) (NN substance)) (VP (VBZ breaks) (PRT (RP down)) (PP (IN into) (NP (NP (DT a) (JJ solid)) (CC and) (NP (DT a) (NN gas)))))) (. .)))
An element cannot be broken down into simpler substances, but the unknown substance breaks down into a solid and a gas.
(ROOT (S (NP (NP (NNS Substances)) (SBAR (WHNP (WDT that)) (S (VP (MD can) (RB not) (VP (VB be) (VP (VBN broken) (PRT (RP down)) (PP (IN into) (NP (NP (JJR simpler) (NNS substances)) (PP (IN with) (NP (JJ different) (NNS properties))))))))))) (VP (VBP are) (VP (VBN called) (NP (NNS elements)))) (. .)))