visual span of sag

例句：

1. 1. The car sags as it hits a bump in the road.
   汽车在遇到路障时下沉。
2. 2. The book sags under its weight.
   这本书因为重量太重而下沉。
3. 3. The bridge is sagging due to years of wear and tear.
   由于多年的磨损，这座桥开始下沉。