The diagrams below show a cross-section of an environment in which there are no earthworms present and a cross-section of an environment in which earthworms are present. Which of the following statements are true of how earthworms affect their environment according to these diagrams?
I. Earthworms increase plant yields.
II. Earthworms decrease the quantity of topsoil.
III. Earthworms are beneficial to their environments.
IV. Earthworms are detrimental to their environments.
A.
I, II, and IV only
B.
II and IV only
C.
I, II, and III only
D.
I and III only