The rain is a very important part of survival of species in the world because millions of people and other number of species id dependent on rain water. The rain when comes brings together the mixture of soil.
What is a mud flow ?
The mud flow is a mixture of water, particles of soil and air. Mud flow is formed when the rain water hits the surface of ground and get mixed with the particles present in the upper layer of soil and the air.
Therefore the substance of mud flow is formed when the "Rain mixes with soil" OPTION A is correct.
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