Final answer:
The ethically correct thing for Mark to do is to tell the teacher about the password and not engage in unauthorized access or use.
Step-by-step explanation:
The ethically correct thing for Mark to do in this situation is option a) Tell the teacher so he may change it. It is important to respect other people's privacy and not engage in unauthorized access or use of their personal information, such as passwords. Mark should understand that breaking into someone else's account is a violation of trust and can have serious consequences.
By notifying the teacher about the situation, Mark is showing integrity and taking responsibility for his actions. This allows the teacher to take appropriate measures to secure her electronic grade-book and prevent any further unauthorized access by anyone.
It is important to always follow ethical principles, such as honesty, respect for others, and responsibility, in any situation. This helps to establish trust and maintain a positive learning environment for everyone involved.