The correct answer is A) indicates that special caution is required. A lateral system buoy displaying a quick light indicates that the mariner should exercise special caution when navigating in that area. This is because a quick light pattern, which flashes more than 120 times per minute, is used to mark areas that require extra vigilance, such as hazards, obstructions, or other navigational challenges. The other options are incorrect because: B) refers to a safe-water mark, C) describes a junction buoy, and D) describes a special-purpose buoy, none of which are specific to a lateral system buoy with a quick light.