( ( Mainstream ( cigarette smoke ) ) ( ( is ( ( a mixture ) ( of ( ( ( ( over 4,000 ) substances ) , ) ( ( 40 ( of which ) ) ( are ( ( ( ( known or ) suspected ) ( ( cancer-causing agents ) ( -LRB- ( carcinogens -RRB- ) ) ) ) ( in humans ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Mainstream) (NN cigarette) (NN smoke)) (VP (VBZ is) (NP (NP (DT a) (NN mixture)) (PP (IN of) (NP (NP (QP (IN over) (CD 4,000)) (NNS substances)) (, ,) (SBAR (WHNP (NP (CD 40)) (WHPP (IN of) (WHNP (WDT which)))) (S (VP (VBP are) (VP (VBN known) (CC or) (VBN suspected) (NP (NP (JJ cancer-causing) (NNS agents)) (PRN (-LRB- -LRB-) (NP (NNP carcinogens)) (-RRB- -RRB-))) (PP (IN in) (NP (NNS humans))))))))))) (. .)))
Mainstream cigarette smoke is a mixture of over 4,000 substances, 40 of which are known or suspected cancer-causing agents (carcinogens) in humans.
(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))))))))))) (. .)))