Which DPD mode on FortiGate will meet the above requirement?

An administrator wants to configure Dead Peer Detection (DPD) on IPSEC VPN for detecting dead tunnels. The requirement is that FortiGate sends DPD probes only when no traffic is observed in the tunnel.

Which DPD mode on FortiGate will meet the above requirement?
A . Disabled
B . On Demand
C . Enabled
D . On Idle

Answer: D

Explanation:

Reference: https://kb.fortinet.com/kb/documentLink.do?externalID=FD40813