Covered ditches are also quite dangerous. Covered ditches are unlikely to cause detection and vigilance. Sometimes there are no dangers on the surface, but they are also hidden dangers. Culverts refer to some drainage facilities or sewers, and the things built on them are actually not safe. After wind and rain erosion, these covered ditches also hide great dangers, in fact, most of them are safety factors. These can be improved through transformation and strengthening, but after all, they belong to a heart disease.
Solemnly declare: the answer is for reference only, please don't be blindly superstitious.