How is high availability of the NSX Edge Gateway accomp…

How is high availability of the NSX Edge Gateway accomplished?

A.
HA Application Monitoring on the Edge Gateway sends a heartbeat to the ESXi host.

B.
VMware Tools on the Edge Gateway sends a heartbeat to the ESXi host.

C.
The Edge appliance sends a heartbeat through an uplink interface.

D.
The Edge appliance sends a heartbeat through an internal interface.

Explanation:
https://www.zettagrid.com/faqs/nsx-charging/