In the IALA Maritime Buoyage System, what is a red and white vertically-striped buoy used to indicate?

Correct Answer: Option D — safe water mark

Safe water marks, defined by IALA, indicate navigable water all around the mark. These buoys are colored with red and white vertical stripes and are typically used to mark fairways, mid-channels, or landfall approaches, as specified in the USCG Navigation Center's IALA Maritime Buoyage System guidelines.