( ( Cigarette smoke ) ( ( ( contains ( ( ( ( more ( than 4,000 ) ) ( different chemicals ) ) , ) ( ( many ( of which ) ) ( are carcinogens ) ) ) ) ( -LRB- ( ( may ( cause cancer ) ) -RRB- ) ) ) . ) )
(ROOT (S (NP (JJ Cigarette) (NN smoke)) (VP (VBZ contains) (NP (NP (QP (JJR more) (IN than) (CD 4,000)) (JJ different) (NNS chemicals)) (, ,) (SBAR (WHNP (DT many) (WHPP (IN of) (WHNP (WDT which)))) (S (VP (VBP are) (ADJP (JJ carcinogens)))))) (PRN (-LRB- -LRB-) (S (VP (MD may) (VP (VB cause) (NP (NN cancer))))) (-RRB- -RRB-))) (. .)))
Cigarette smoke contains more than 4,000 different chemicals, many of which are carcinogens (may cause cancer).
(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))))))))))) (. .)))