In Apex, the IsUpdateable() method of the Schema.DescribeFieldResult class checks if the current user has permission to update a specific field. Using this method ensures that the Apex class respects Field-Level Security (FLS) for all profiles, avoiding unauthorized updates.

Option A: Adding the "With Sharing" keyword enforces record-sharing rules but does not enforce field-level security.

Option B: Placing the code in an inner class with "With Sharing" does not address the field-level security issue.

Option C (Correct): Using IsUpdateable() ensures field permissions are honored programmatically, preventing updates to read-only fields.