horseshoe sewer

例句：

1. 1. The city has been working on improving its horseshoe sewer system for years.
   这个城市多年来一直在努力改善其马蹄形下水道系统。
2. 2. The construction of the new roads will require the removal of several horseshoe sewers.
   新道路的建设将需要移除几个马蹄形下水道。
3. 3. The horseshoe sewer was a common feature in old cities, but now it's rare to see them.
   马蹄形下水道是旧城市的一个常见特征，但现在很少见了。