Which domain controller should you identify?

Your network contains an Active Directory forest. The forest contains two domains named
contoso.com and corp.contoso.com. The forest contains four domain controllers. The domain
controllers are configured as shown in the following table

All domain controllers are DNS servers. In the corp.contoso.com domain, you plan to deploy a new
domain controller named DC5.
You need to identify which domain controller must be online to ensure that DC5 can be promoted
successfully to a domain controller.
Which domain controller should you identify?

A.
DC1

B.
DC2

C.
DC3

D.
DC4