When are you in danger when overtaking?

You answered correctly. When overtaking, you are at risk if the vehicle in front of you suddenly accelerates or swerves out to overtake. Both actions can make overtaking unsafe because your distance and speed calculations are disrupted. If the vehicle moves sideways or increases its speed unexpectedly, it can force you into a dangerous situation or prevent you from overtaking safely. However, if the vehicle in front simply reduces its speed considerably, it generally makes overtaking easier and safer, not more dangerous. This is why only the first two situations are correct in this context. Always watch for signs that the car in front may change speed or direction before overtaking.