问题如下：
Suppose the cost of producing tea relative to copper is lower in Tealand than in Copperland. With trade, the copper industry in Copperland would most likely:
选项：
A.expand.
B.contract.
C.remain stable.
解释：
A is correct.
The copper industry in Copperland would benefit from trade. Because the cost of producing copper relative to producing tea is lower in Copperland than in Tealand, Copperland will export copper and the industry will expand.
考点：比较优势
解析：在Tealand 国家，TEA相较于黄铜的生产成本比较低。那Tealand 就该生产TEA。那么 Copperland 就应该生产黄铜。那就应该扩大生产黄铜，选A。
理解成一国的 tea/copper的成本低于另一国了，什么时候才判断是机会成本的表达呢？
