A Server Has a File Share for Each Department

A server has a file share for each department. An auditor has discovered that all users have access to all of the departmental shared folders. Which of the following is the BEST solution to ensure users have access to the shared folders of only their department?

A) Create security groups, add the users to the security groups according to their departments, and grant the security groups access to the file shares according to each department.
B) Delete the shared folders and create new shared folders, and grant the users access to the shared folders according to their departments.
C) Remove everyone from the shared folders, create a security group for each department, add the users to the security groups, and grant each security group access to its own shared folders.
D) Remove everyone from the shared folders, grant full access to the IT administrators, and instruct the users to ask managers permission to be re-added to the shared folders according to their department.