You isolate an infectious substance capable of causing disease in plants, but you do not know whether the infectious agent is a bacterium, virus, viroid, or prion. You have four methods at your disposal to analyze the substance and determine the nature of the infectious agent. I. Treat the substance with enzymes that destroy all nucleic acids and then determine whether the substance is still infectious.
II. Filter the substance to remove all elements smaller than what can be easily seen under a light microscope.
III. Culture the substance on nutritive medium, away from any plant cells.
IV. Treat the sample with proteases that digest all proteins and then determining whether the substance is still infectious.

If you already know that the infectious agent was either bacterial or viral, which method(s) listed above would allow you to distinguish between these two possibilities.

a. I only
b. Il only
c. Ill only
d. IV only
e. either I or IV