( ( As ( ( experts ( in chemistry ) ) know ) ) ( , ( ( ( a catalyst ) ( by itself ) ) ( ( ( can not ) ( ( provoke ( a ( meaningful reaction ) ) ) ( if ( ( other ( ( elements or ) substances ) ) ( are ( ( missing or ) insufficient ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN As) (S (NP (NP (NNS experts)) (PP (IN in) (NP (NN chemistry)))) (VP (VBP know)))) (, ,) (NP (NP (DT a) (NN catalyst)) (PP (IN by) (NP (PRP itself)))) (VP (MD can) (RB not) (VP (VB provoke) (NP (DT a) (JJ meaningful) (NN reaction)) (SBAR (IN if) (S (NP (JJ other) (NNS elements) (CC or) (NNS substances)) (VP (VBP are) (ADJP (JJ missing) (CC or) (JJ insufficient))))))) (. .)))
As experts in chemistry know, a catalyst by itself cannot provoke a meaningful reaction if other elements or substances are missing or insufficient.
(ROOT (S (NP (PRP You)) (VP (VBP call) (NP (NP (DT a) (NN substance)) (SBAR (WHNP (WDT that)) (S (VP (MD can) (RB not) (VP (VB be) (VP (VBN broken) (PRT (RP down)) (PP (TO to) (NP (JJ other) (NNS substances))) (PP (IN by) (NP (NP (NN chemical) (NNS reactions)) (NP (DT an) (NN element))))))))))) (. .)))