tunnel portal的用法和樣例：
例句
- He ran down the circular stairs and got to the entrance to the tunnel just as DeLisio got to the tower.
就在德萊索上塔同時，他跑下旋轉梯，奔隧道口而去。 - Without the tunnel mouth being properly set up a derailed train will bounce off an invisible barrier when it tries to pass under the ground.
如果沒有適當的設置隧道口，一列出軌的列車將在進入隧道試圖穿過地面進入地下時被看不見的柵欄彈回。
