这座山形成了两个村庄之间的自然分界线。

The mountain serves as the natural ___boundary between the two villages.

这项新技术正在突破医学治疗的极限。

This new technology is pushing the ___boundaries of medical treatment.

击球手击出一记完美的边界球，立即获得四分。

The batter hit a perfect ___boundary to score four runs instantly.