What is the role of oceans in the nitrogen cycle?

I- Oceans have no role in the nitrogen cycle.
II- Only some species of cyanobacteria fix nitrogen in oceans.
III- Anammox bacteria are responsible for converting nutrients into gaseous nitrogen in oceans.
IV- Trichodesmium is the main agent responsible for fixing nitrogen in oceans.
a) I and III are correct.
b) II and IV are correct.
c) II and III are correct.
d) III and IV are correct.
e) I and II are correct.