( ( At ( ( ( ( ( ( present six ) kinds ) ( of leptons ) ) ( -LRB- ( ( that ( ( is , ) ( six ( lepton flavors ) ) ) ) -RRB- ) ) ) and ) ( ( six kinds ) ( of quarks ) ) ) ) ( ( -LRB- ( ( six ( quark flavors ) ) -RRB- ) ) ( ( are known ) . ) ) )
(ROOT (S (PP (IN At) (NP (NP (NP (ADJP (JJ present) (NP (CD six))) (NNS kinds)) (PP (IN of) (NP (NNS leptons)))) (PRN (-LRB- -LRB-) (SBAR (WHNP (WDT that)) (S (VP (VBZ is) (, ,) (NP (CD six) (NN lepton) (NNS flavors))))) (-RRB- -RRB-)) (CC and) (NP (NP (CD six) (NNS kinds)) (PP (IN of) (NP (NNS quarks)))))) (PRN (-LRB- -LRB-) (NP (CD six) (NNP quark) (NNS flavors)) (-RRB- -RRB-)) (VP (VBP are) (VP (VBN known))) (. .)))
At present six kinds of leptons (that is, six lepton flavors) and six kinds of quarks (six quark flavors) are known.
(ROOT (S (NP (EX There)) (VP (VBP are) (NP (NP (CD six) (NNS types)) (PP (IN of) (NP (NNS leptons))))) (. .)))