According to the nebular hypothesis, when did nuclear fusion begin?

According to nebular hypothesis, the solar system was formed 4.5 billion years ago in solar nebula.

The solar nebula- a molecular cloud of dust and gases collapsed under its own gravity. In order to conserve momentum, this collapsed core started spinning while gathering more and more mass. The temperature and pressure rose. When sufficient temperature and pressure is achieved, nuclear fusion reaction kicks in. While the rest of the part formed proto-planetary disk.

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; the correct answer is (beta)