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Frontier
01
边境
the outer edge of occupied or developed land, beyond which lies unsettled territory
02
边境
an undeveloped field of study; a topic inviting research and development
03
边境
an area located at a border, where two countries or regions meet
例子
Speculators and prospectors often ventured ahead of the settled frontier in search of fertile lands and mineral wealth.
Pioneers migrated westward, steadily pushing the frontier of settlement into new territories.
During the 19th century, settlers pushed west across the Great Plains, gradually expanding the frontier of the young American nation.
European explorers pushed back the frontiers of the known world by discovering new continents.
The westward expansion of the United States in the 19th century pushed the frontiers of the nation.
