Frontier is a noun that refers to the border between two countries or a border region. It can also refer to the area of America in the west that was not settled by Europeans before the 20th century, or the edge or limit of a field, especially in knowledge or science.
frontier 是一个名词,表示国家之间的边界或边境。它还可以指 20 世纪前美国西部未被欧洲移民定居的地区,或知识、科学等领域的前沿或尖端。
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