What is the purpose of tumor markers?

I- To guide treatment decisions.
II- To monitor treatment progress.
III- To predict the likelihood of recovery.
IV- To diagnose cancer in people at high risk of developing the disease.
a) Only I and II are correct.
b) Only I, II, and III are correct.
c) Only I, II, and IV are correct.
d) I, II, III, and IV are correct.