What is the source of the problem?

A vSphere Administrator notices that the newly deployed ESXi hosts cannot stay in a connected state in
vCenter Server for more than 60 seconds at a time. The Administrator knows that the hardware is in good
health and that the ESXi hypervisors are properly configured.
What is the source of the problem?

A.
The hosts are not a part of a vSphere Distributed Switch.

B.
Firewall rules that have too many ports open.

C.
Firewall rules preventing hosts from sending heartbeats to vCenter Server.

D.
The hosts do not have persistent logging configured.

Explanation:
https://kb.vmware.com/selfservice/search.do?
cmd=displayKC&docType=kc&docTypeID=DT_KB_1_1&externalId=1029919