Under the IALA cardinal system, a mark with a quick white light showing 6 flashes followed by one long flash indicates that the safest water is on the __________.

Correct Answer: Option D — south side of the mark

A South Cardinal mark is characterized by a light showing 6 flashes followed by one long flash. This signal indicates that the safest water is located to the south of the mark. Mariners should pass to the south of the buoy to avoid the danger located to its north.