Question

Erosion _________ when the amount of vegetation _________.

Answer 1

None of the above.

Erosion is more likely to increase when the amount of vegetation decreases.  The potential for soil erosion increases if the soil has no or very little vegetative cover of plants.

Plants and their residue form a cover that protects the soil from direct raindrop impact and splash, tending to slow down movement of runoff water and allows excess surface water to infiltrate, preventing erosion by water.

Plants root systems tend also to anchor top soil in place such that  it is firm and  cannot be easily blown away by wind thus preventing erosion by wind.