Yes, the correct answer is D. "cepillarme". In the given statement, the person is saying "Let's go to the movies now!" and then explaining that they cannot leave yet because they still need to do something first. The phrase "Primero debo" indicates that they need to do an action. In this case, the action is related to their teeth, so "cepillarme" which means "brush my teeth" is the most appropriate choice.
