You are underway in the North Sea on course 216°T when you sight a buoy bearing 021° relative. Under the IALA Buoyage System, you are in the best navigable water if the buoy has which of the following characteristics?

Correct Answer: Option B — has a light characteristic of Q(6) + L Fl 15s

Under IALA rules, Q(6) + L Fl 15s represents a South cardinal mark. A vessel in the North Sea observing this relative bearing is in best navigable water when passing south of the mark, corresponding to the indicated light signature.