Under the IALA Buoyage System, which topmark shown in illustration D023NG below will be displayed on a safe water mark?

Correct Answer: Option A — A

IALA Buoyage System standards dictate that a safe water mark, often called a fairway buoy, is identified by a single red sphere topmark. This distinct shape distinguishes it from lateral marks and isolated danger marks, ensuring mariners recognize the mark as indicating navigable water all around the buoy.