( ( Cigarette smoke ) ( ( contains ( thousands ( of ( ( ( different chemicals ) , ) ( ( many ( of which ) ) ( are ( ( proven carcinogens ) ( -LRB- ( ( cancer ( causing agents ) ) -RRB- ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Cigarette) (NN smoke)) (VP (VBZ contains) (NP (NP (NNS thousands)) (PP (IN of) (NP (NP (JJ different) (NNS chemicals)) (, ,) (SBAR (WHNP (DT many) (WHPP (IN of) (WHNP (WDT which)))) (S (VP (VBP are) (NP (NP (VBN proven) (NNS carcinogens)) (PRN (-LRB- -LRB-) (NP (NP (NN cancer)) (S (VP (VBG causing) (NP (NNS agents))))) (-RRB- -RRB-)))))))))) (. .)))
Cigarette smoke contains thousands of different chemicals, many of which are proven carcinogens (cancer causing agents).
(ROOT (S (NP (NNS Cigarettes)) (VP (VBP are) (NP (NP (DT a) (JJ major) (NN source)) (PP (IN of) (NP (NP (NNS carcinogens)) (, ,) (NP (NP (DT a) (NN kind)) (PP (IN of) (NP (NP (NN chemical) (NNS substances)) (VP (VBN linked) (PP (IN with) (NP (NN cancer))))))))))) (. .)))