( ( Tin ( must ( be ( ( ( mined ( -LRB- ( ( mainly ( as ( the ( tin ( ore cassiterite ) ) ) ) ) -RRB- ) ) ) and ) ( smelted separately ) ) ) ) ) ( , ( then ( ( added ( to ( ( molten copper ) ( to ( make ( bronze alloy ) ) ) ) ) ) . ) ) ) )
(ROOT (S (S (NP (NN Tin)) (VP (MD must) (VP (VB be) (VP (VP (VBN mined) (PRN (-LRB- -LRB-) (PP (ADVP (RB mainly)) (IN as) (NP (DT the) (NN tin) (NN ore) (NN cassiterite))) (-RRB- -RRB-))) (CC and) (VP (VBN smelted) (ADVP (RB separately))))))) (, ,) (NP (RB then)) (VP (VBD added) (S (VP (TO to) (VP (VB molten) (NP (NN copper)) (S (VP (TO to) (VP (VB make) (NP (NN bronze) (NN alloy))))))))) (. .)))
Tin must be mined (mainly as the tin ore cassiterite) and smelted separately, then added to molten copper to make bronze alloy.
(ROOT (S (NP (NN Bronze)) (VP (VBZ is) (NP (NP (DT an) (NN alloy)) (PP (IN of) (NP (NN copper) (CC and) (NN tin))))) (. .)))