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(shí)，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(méi)有適當的設置隧道口，一列出軌的列車(chē)將在進(jìn)入隧道試圖穿過(guò)地面進(jìn)入地下時(shí)被看不見(jiàn)的柵欄彈回。
