Why is it to study embryonic structures when determining evolutionary relationships?

Vestigial structures do not have a function, yet they are homologous to functional structures in related species. They are important because they provide clues to the ancestry of the organism. Many species look similar as embryos.

answer: tributaries flow into rivers.

wetland is a biome that develops when the water gets accumulated in a land exhibiting a huge depression. these form either seasonally or permanently. the water in the wetland comes from rivers, lakes, ocean, flood, rain or other sources. the wetlands includes mangroves, marshes and peatland.

tributaries flow into the rivers develops a wetland because such water will get deposited in the depression and will restrict the original flow of tributary water. hence, water with low drainage current combines with the river water.

answer; i believe the answer is hydraulic action;