The principal has cancelled the prom. You are trying to persuade him/her to reconsider his/her decision. Using ethos logos or pathos

you are attempting to convince your parents to buy you a pet rabbit

The answer here is "Pathos."

Ethos, Logos and Pathos are terms coined by Aristotle to define how individuals persuade or convince another to an action. Ethos focuses on self good and credible character to convince or persuade. Logos however is based on logic or reason. In this instance, the individual is likely to use supporting documents, research and facts to convince. Pathos, however focuses on appealing to the emotion of the other, so that they can have some sympathy.