( ( An element ) ( ( is ( ( a ( pure substance ) ) ( which ( ( can not ) ( be ( ( ( broken down ) ( into ( simpler substances ) ) ) ( by ( chemical means ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT An) (NN element)) (VP (VBZ is) (NP (NP (DT a) (JJ pure) (NN substance)) (SBAR (WHNP (WDT which)) (S (VP (MD can) (RB not) (VP (VB be) (VP (VBN broken) (PRT (RP down)) (PP (IN into) (NP (JJR simpler) (NNS substances))) (PP (IN by) (NP (NN chemical) (NNS means)))))))))) (. .)))
An element is a pure substance which cannot be broken down into simpler substances by chemical means.
(ROOT (S (NP (PRP You)) (VP (VBP call) (NP (NP (DT a) (JJ pure) (NN substance)) (SBAR (WHNP (WDT that)) (S (VP (MD can) (RB not) (VP (VB be) (VP (VBN broken) (ADVP (RB down) (PP (IN into) (NP (NP (JJ different) (NNS types)) (PP (IN of) (NP (NNS substances)))))) (NP (DT a) (PRN (-LRB- -LRB-) (NP (NN n)) (-RRB- -RRB-)) (NN element))))))))) (. .)))