Final answer:
Upon learning that a teacher cannot make it last minute, the correct action is to inform the principal so they can manage the situation.
Step-by-step explanation:
If you receive a call the morning of class that your teacher cannot make it last minute, the appropriate action would be to inform the principal, as they would take the necessary steps to manage the situation. This may include contacting a substitute teacher or rearranging the classroom schedule.
While quickly preparing a lesson plan or gathering teaching materials might be helpful, these steps would typically be undertaken by a substitute teacher who may already have instructions from the absent teacher. Additionally, you may not have the authority or access to contact the substitute teacher directly.