Eustress refers to positive stress that can motivate you and help you feel energized or excited about a situation. In the scenarios listed, none perfectly exemplify eustress as they all depict negative stress responses. However, if we had to choose one that could be interpreted as having a potential positive outcome (assuming you're excited about graduating), scenario C (waiting in line to accept your high school diploma) might lean closer to eustress, as it represents a significant achievement and the excitement that can come from such an event, even though it may also create nerves.
Consideration: Eustress shouldn’t be overly overwhelming or detrimental to your well-being, which can often be case with the other scenarios provided.