manhole with sight glass

例句：

1. 1.The manhole was covered with a layer of dirt.
   那个地洞被一层泥土覆盖着。
2. 2.He climbed down the ladder and opened the manhole.
   他爬下梯子，打开了那个地洞。
3. 3.The manhole led to a small tunnel.
   那个地洞通向一个小隧道。