The set consists of nine coins: three in gold, five in silver, and one copper-alloy coin.

3、5、以及1铜。

But more modern builders stopped using copper and copper alloys. They cost more than other building materials.

但是现代建筑师已不再用铜和铜，因为它们比其他建筑料都要贵。

Keevil says earlier generations of builders in the United States also knew this about copper. That is why copper alloys such as brass were often used in building materials.

基维尔说美国早期的建筑师们也知道铜的这种用法，因此黄铜等铜被用做建筑料。

It also grew out of thousands of years of development of simple furnaces to make pottery, and then to extract copper ores and work copper alloys (bronzes) that do not require as high temperatures as does iron.

它也源于数千年来用于制造陶器的简单熔炉的发展，然后提取铜矿石并加工不需要像铁那样高温的铜（青铜）。