Final answer:
The appropriate action for a boat being overtaken by another in darkness or reduced visibility is to maintain course and speed to ensure safety and prevent collisions.
Step-by-step explanation:
When a boat is being overtaken by Boat A in darkness or reduced visibility, the action that is required of the overtaken boat is to maintain course and speed. This is a standard rule of navigation to prevent collisions at sea. Increasing speed to avoid being overtaken or changing course could lead to confusion and increase the risk of an accident. Sound signals or lights specific to the situation, such as those for vessels in restricted visibility, would be used, but these are not options provided in the question. The green light on the starboard side, while it must be shown, is part of routine navigation lighting and not a specific action to take when being overtaken.