Which downstream FortiGate VDOM is used to join the Security Fabric when split-task VDOM is enabled on all FortiGate devices?
A. FG-traffic VDOM
B. Root VDOM
C. Customer VDOM
D. Global VDOM
Reference: https://docs.fortinet.com/document/fortigate/6.2.0/new-features/287377/split-task-vdom-support