What are vessels required to display according to Rule 20?

Answer: B — Proper lights and shapes according to their type and activity

Vessels are required to display proper lights and shapes according to their type and activity as stipulated in Rule 20 of the COLREGs. This rule is essential for ensuring safety on the water, particularly during times of reduced visibility such as at night or in fog. The display of appropriate navigation lights and shapes allows for other vessels to recognize their type, activity, and status, thereby preventing collisions and facilitating safe navigation. For instance, different kinds of vessels (like fishing boats, sailing ships, and powerboats) have specific light arrangements and shapes they must display. These signals indicate to others if they are under sail, undergoing fishing activities, or anchored, among other scenarios. The other options do not align with the requirements set forth in Rule 20. The display of flags based on nationality, emergency lights, or a unique identification number relates to different regulations and does not pertain directly to the requirements for lights and shapes that enhance navigational safety outlined in this rule.