( This ( ( ( ( corresponds ( to ( ( the grade ) ( of ( a ( metal ore ) ) ) ) ) ) , ) ( for instance ) ) . ) )
(ROOT (S (NP (DT This)) (VP (VBZ corresponds) (PP (TO to) (NP (NP (DT the) (NN grade)) (PP (IN of) (NP (DT a) (NN metal) (NN ore))))) (, ,) (PP (IN for) (NP (NN instance)))) (. .)))
This corresponds to the grade of a metal ore, for instance.
(ROOT (S (NP (NNS Metals)) (VP (VBP start) (PRT (RP out)) (PP (IN as) (NP (NN ore)))) (. .)))
Metals start out as ore.