I think you should tell the reason for the lack of actual class. If you have a good reason for missing class, your teacher probably isn't what you and the teachers probably understand you more.
I think you should tell the real reason for their absence. If you have a good reason for the lack of teachers and teacher, you do not say anything you would understand you more.
I think you should tell the reasons of absent real If you have a good reason to be absent teacher in your mind you and the teacher can understand you better.