How are these homologous structures evidence of an evolutionary relationship?

A common ancestor

Explanation: Homologous structures in different species could suggest that they shared a common ancestor.

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.

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.