(While) copper, (unlike gold) , ( is not considered) a glamorous metal, it (has long been) one of the world’s valuable commodities.
The answer is E (No error). Why is the error not A? shouldn’t it be although? Why is it allowed to be while?
It’s almost universally accepted that “while” can be used in that way. Is this an official question? If so, now you know that the College Board considers that usage acceptable.