The answer is: B
Explanation
The principle that applies to the given scenario is that a country's laws apply to ships flying its flag or aircraft registered with it, and on persons on board these carriers. This principle is known as the flag state principle.
In the given scenario, the ship is registered in Country A and flying the flag of Country A. Therefore, according to the flag state principle, the laws of Country A apply to the accused.
Option A is incorrect because only one country can prosecute the accused. Option C is incorrect because not every country has jurisdiction over the ship. Option D is incorrect because the nationality of the victim does not determine which country has jurisdiction over the accused. Option E is incorrect because international law does not allow for a legal vacuum in international waters.
Therefore, option B is correct.