If a vessel overtakes another, which vessel is the stand-on vessel?

Answer: B — The vessel being overtaken

In an overtaking situation, the vessel being overtaken is the stand-on vessel. This is because the overtaking vessel must keep out of the way and pass safely, while the vessel being overtaken should maintain its current course and speed unless there’s a collision risk. The stand-on vessel isn’t expected to alter course or speed just because another vessel is overtaking; it continues on its path unless acting to avoid danger. So, the vessel being overtaken is the stand-on vessel.