I would go with A. B would come next. So yeah A
It is c because it will have a more positive connotation.
Social Media, letters, suggestions.
My personal recommendations would be to
A ) Make the subject shorter, like "Reason for Absence" or "My Absence"
B ) Make the email more formal. (You don't have to copy my recommendation word for word but if you want to or use it for reference that works):
"Good Morning/Afternoon/Evening Mrs. __,
I hole you're have a lovely morning/afternoon/evening. Today I was absent and I apologize for the inconvenience. The class meeting didn't appear on my canvas courses and I couldn't find a zoom link. If there's anywhere I can find either one for the future please let me know and again I'm sorry for the inconvenience.
Sincerely,
__"
