In the Health Cloud data model for Activity Planning, a many-to-many relationship exists between Activity Plans and Territories. This relationship is managed through a junction object. The correct API name for this junction object is ActivityPlanTerritory. To make an Activity Plan active for a specific sales territory, a record must be created in this object to link the ActivityPlan record with the corresponding Territory2 record.

B. Territory Activity Plan: This is an incorrect name for the junction object. Salesforce object naming conventions are precise.

C. Territory Plan Assignment: This is a plausible but incorrect name. The standard object is ActivityPlanTerritory.

Salesforce Help, Health Cloud Administrator Guide, "Assign Activity Plans to Territories". This documentation explicitly states that to associate a plan with a territory, you create an ActivityPlanTerritory record.

Salesforce Object Reference for Salesforce and Lightning Platform, "ActivityPlanTerritory". The official object reference guide defines ActivityPlanTerritory as the junction object that represents the association between an ActivityPlan and a Territory2 (Territory).