( ( The Sumerians ) ( ( invented ( ( bronze , ) ( ( an alloy ) ( of ( ( copper and ) tin ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NNPS Sumerians)) (VP (VBD invented) (NP (NP (NN bronze)) (, ,) (NP (NP (DT an) (NN alloy)) (PP (IN of) (NP (NN copper) (CC and) (NN tin)))))) (. .)))
The Sumerians invented bronze, an alloy of copper and tin.
(ROOT (S (NP (NN Bronze)) (VP (VBZ is) (NP (NP (DT an) (NN alloy)) (PP (IN of) (NP (NN copper) (CC and) (NN tin))))) (. .)))