To minimize pollution, factories should be built . -Along the river
-In the middle of the town
-Downstream from all towns and cities
-Upstream from all towns and cities

Downstream, along the river is vague and middle of town makes no sense, upstream would mean that the pollution would run right past the town and cities and could pollute the town's and cities

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.