The correct answer is C. 64.26.151.37 .

The study guide explains the FortiGuard flags shown by diagnose debug rating:

D = Default

I = Initial

T = Timing

F = Failed and specifically: “F = The server is down”

So even though 121.111.236.179 has the lowest RTT in the exhibit, it has the F flag, meaning FortiGate considers that server failed/down , so it will not be chosen.

To determine which active server is selected, the FortiOS administration guide states:

“The server list is sorted first by weight. The server with the smallest RTT appears at the top of the list regardless of weight. … Therefore the top position in the list is selected based on RTT while the other positions are based on weight.”

Among the valid, non-failed choices in the exhibit:

64.26.151.37 → RTT 45

209.22.147.36 → RTT 103

96.45.33.65 → RTT 144

208.91.112.194 → RTT 107

The active server with the lowest RTT is 64.26.151.37 , so that is the server FortiGate will choose.

So the verified answer is: C .