In which cases must you abandon overtaking?

You answered correctly. You must abandon overtaking if the vehicle you are passing suddenly accelerates or if there is unexpected oncoming traffic creating a danger. These situations make overtaking unsafe, so the maneuver should be stopped immediately to prevent accidents. However, if the vehicle being overtaken slows down considerably, this alone does not require you to abort overtaking, as it could make passing easier and safer. Always prioritize safety and be ready to stop overtaking whenever the situation on the road changes and introduces risk.