Which sharing model provides the most restrictive access to records?

Correct answer: Private

Option A is correct because the Private organization-wide default sharing setting restricts record access so that only the record owner and users higher in the role hierarchy can view or edit records, making it the most restrictive baseline in Salesforce sharing. Option B is incorrect because Controlled by Parent means a record's access is determined by the parent record's sharing setting, which may itself be private, but this is a dependent setting used for detail objects rather than the most restrictive standalone choice. Option C is incorrect because Public Read/Write allows all users in the organization to view and edit all records of that object, which is the most permissive setting. Option D is incorrect because Public Read Only allows all users to view records but restricts editing to the owner and hierarchy, making it less restrictive than Private.