Commemorative plaques cast from brass are a characteristic art form of the Benin culture of West Africa. Some scholars, noting that the oldest surviving plaques date to the 1400s, hypothesize that brass-casting techniques were introduced by the Portuguese, who came to Benin in 1485 A.D. But Portuguese records of that expedition mention cast-brass jewelry sent to Benin`s king from neighboring Ife. So it is unlikely that Benin`s knowledge of brass casting derived from the Portuguese.Which of the following, if true, most strengthens the argument?
【选项】Copper, which is required for making brass, can be found throughout Benin territory.