Soil which is moderately permeable is helpful in preventing erosion. This is because the moderately permeable soil will A. easily support a great deal of vegetation, preventing runoff.
B. allow water to soak in easily, preventing runoff.
C. easily level out so that the slope of the land is decreased.
D. increase the rate of evaporation.

B. allow water to soak in easily, preventing runoff.

Explanation:

Soil Permeability is the ease at which water and air go into soil. A moderately permeable soil will therefore allow water and air to go to it easier and this prevents soil erosion.

Soil erosion from water happens when there is runoff but this will be less with moderately permeable soils because the water will sink into the ground faster and so will not runoff and carry the topsoil with it thereby preventing erosion.