The correct option is
C erosion
Option C: 'Erosion' is a noun that refers to 'the process by which the surface of the earth is worn away by the action of winds, waves, glaciers, etc.'
(Trees prevent 'soil erosion'.) Hence option C is correct.
Option A: 'Eroded' is a past verb that refers to an action that has already happened. But the sentence presents a general truth and a specific past event is not mentioned.
Option B: 'Erose' means 'gnawed away'. The meaning is irrelevant to the given sentence.
Option D: The word 'erodion' does not exist in the standard English language.
Hence options A, B and D are incorrect.