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 __________.

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

The light characteristic Q(6) + L Fl 15s identifies a South cardinal mark under the IALA system. South cardinal marks indicate that the safest water lies to the south of the mark. Since you are on course 216°T and the buoy is to your north, passing south of it keeps you safe.