an underground的用法和樣例：
例句
- An underground bed or layer of earth, gravel, or porous stone that yields water.
地下蓄水層，砂石含水層含有水的泥、砂礫或多孔石的地下河床或地層 - An underground defensive position with a fortified projection above ground level for gun emplacements.
掩蔽壕，地堡一個地下防禦工事，有一個高幹地面的，用來放槍的防禦射擊處 - There is an underground car park near the supermarket.
這個超市附近有一個地下停車場。 - The prisoner escaped by digging an underground tunnel.
囚犯挖了一條地道逃跑了。
