What is possible cause for this error?

An IaaS Administrator is trying to add a new vCenter endpoint. When the administrator clicks “Test Connection”, the attempt fails with the following error:

What is possible cause for this error?
A . The service account password is using invalid special characters.
B . The IaaS administrator entered an incorrect vCenter fully qualified domain name (FQDN) in the vCenter address.
C . The service account for the vCenter endpoint has not been assigned a role in vCenter.
D . The service account was entered in user principal name (UPN) format.

Answer: A

Explanation:

Reference: https://docs.vmware.com/en/vRealize-Automation/7.5/com.vmware.vra.prepare.use.doc/GUID3051E04E-C809-4E29-A3BF-51053BB2D7BC.html