While viewing the Electron Transport Chain simulation in Labster, it showed how electrons from electron carriers are 'dropped off' at the beginning of the process. Why did it show two different pathways electrons can take during this simulation

Electrons can be either passed on to the electron transport chain by NADH⁺ at the first complex (NADH⁺-coenzyme Q oxidoreductase) or at the second complex(FADH⁺-coenzyme Q oxidoreductase). I think that's what you're referring to.

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.