In the context of SAP Ariba integration via CIG, what is a subaccount user or account user in the SAP Cloud Connector integrator?

In the context of SAP Ariba integration via CIG, what is a subaccount user or account user in the SAP Cloud Connector integrator?
A . S-User for your customer account with SAP
B . SAP ERP system user ID
C . P-User of SAP Ariba Cloud Integration Gateway
D . Ariba Network admin user

Answer: C