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Ahthough copper was hammered into toos and ornaments by some early inhibitants of North America,the smelting and casting of copper were unkown between them.
Answer d) between->among.
My question:it is (the smelting and casting of copper),not (the smeting and the casting of copper),so (were ->was).
我记得：the smelting and casting of copper应该按单数处理吧？ | 
