How can these requirements be met?

Universal Containers sales reps can modify fields on an opportunity until it is closed. Only the sales operation team can modify the post closed follow-up dates and post closed follow-up comments fields.

How can these requirements be met?
A . Use record types with field sets and restrict editing fields using field-level security.
B . Use field-level security on page layouts to restrict editing fields
C . Use multiple record types, page layouts and profiles.
D . Use field level security to mark fields as read only on the sales profile

Answer: B