DRAG DROP
You are researching integrations with several external systems.
Each integration has different requirements.
You need to determine which data sources to use to meet each requirement.
What should you use? To answer, drag the appropriate data sources to the correct requirements. Each data source may be used once, more than one, or not at all. You may need to drag the split bar between panes or scroll to view content.
NOTE: Each correct selection is worth one point.
Answer: 
Explanation:
Box 1: Virtual entity
Initially, defining a virtual entity is the same as defining a custom entity: you specify the entity, attributes, and relationships for the new virtual entity type.
You can use GUIDs as primary keys in the external data source.
Box 2: Virtual entity
Virtual entities enable the integration of data residing in external systems by seamlessly representing that data as entities in Microsoft Dataverse (Common Data Service), without replication of data and often without custom coding. Virtual entities support create, updates and delete of data in the external system.
Box 3: Custom connector
A custom connector is a wrapper around a REST API (Logic Apps also supports SOAP APIs) that allows Logic Apps, Power Automate, or Power Apps to communicate with that REST or SOAP API.
Reference:
https://docs.microsoft.com/en-us/powerapps/developer/common-data-service/virtual-entities/get-started-ve