( ( Brass ( which ( is ( ( an alloy ) ( of ( ( copper and ) zinc ) ) ) ) ) ) ( , ( ( ( was not ) ( known ( till ( the ( thirteenth century ) ) ) ) ) . ) ) )
(ROOT (S (NP (NP (NNS Brass)) (SBAR (WHNP (WDT which)) (S (VP (VBZ is) (NP (NP (DT an) (NN alloy)) (PP (IN of) (NP (NN copper) (CC and) (NN zinc)))))))) (, ,) (VP (VBD was) (RB not) (VP (VBN known) (PP (IN till) (NP (DT the) (JJ thirteenth) (NN century))))) (. .)))
Brass which is an alloy of copper and zinc, was not known till the thirteenth century.
(ROOT (S (NP (NNP Brass) (NNP alloy)) (VP (VBZ is) (VP (VBN made) (PP (IN from) (NP (NN copper) (CC and) (NN zinc))))) (. .)))