Although copper was hammered into tools and ornaments by some early inhabitants of North America, the smelting and casting of copper were unknown among them.
如果the smelting and casting of copper 改成the smelting and the casting of copper那后面的动词用were当然没意见,但是现在的情况就好象我们中学讲的:a famous actor and singer一样了,可以看成是一个东西的两个特点,因为只有一个冠词。所以说我觉得were应该改成was。
不过我是这么想的,如果要是分开的意思的话,那难道不应该是用the smelting and the casting of copper么?要不就一个the 怎么指代后面的casting?我觉得and连接同样的成分,所以casting只和smelting 并列,但同时它又不能没有the 的修饰,所以只有把两个工艺连在一起当一个加工过程讲??