Universal Containers has implemented Customer Community with Customer Community Plus licenses for its distributors.

Sharing Sets in Customer Communities:

Sharing Sets provide a scalable way to grant access to records based on a user's relationship to the record. In this case, the account contact relationship can be used to determine which distributor accounts the part-time agents can access.

Why Option A is Correct:

Sharing Sets are ideal for Community Plus licenses, allowing access to related distributor accounts without needing complex customization.

Agents can access other distributor accounts through their account contact relationship.

Why Others Are Incorrect:

Option B (Apex Sharing): Apex Sharing adds unnecessary complexity for this use case when Sharing Sets are sufficient.

Option C (Sharing Rules): Sharing Rules do not work with the account contact relationship in the context of Community Plus licenses.

For more information, see Salesforce Sharing Sets documentation: https://help.salesforce.com/