The processes that change the boulder and cobbles to soil are weathering and (a) metamorphism (b) biological activity (c) cementation of sediments (d) melting of rock material

(B) biological activity

Explanation:

The processes that change the boulder and cobbles to soil are weathering and biological activity. Weathering is the process in which the weather breaks down rocks into smaller pieces and particles, whether if it is from water, air or living organisms. Various biological processes help facilitate rock fragmentation. Between them we may find the roots of the trees that eventually pull rocks apart, we find how animals walk through the rocks making them disintegrate, and finally, we find some organisms that release chemicals that help break rocks.

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