There is a Trap here... C and D have something right but the trick is the question...
Under SSL VPN settings you can see that port is 443 (same of https admin port) BUT the question is about a SSL VPN Setting FOR A VPN PORTAL... so if you go to SSL VPN Portals and hit "Create new" you will see Tunnel Mode and Split Tunnel enabled by default... so, the correct answer is C.
Split tunneling is a feature that allows a remote VPN user to tunnel only specific, protected traffic back to the corporate network, while other traffic (e.g., internet traffic) is sent directly to its destination. This can help optimize bandwidth usage and reduce the load on the corporate network.
In the context of SSL VPN settings for an SSL VPN portal on FortiGate, if split tunneling is enabled by default, it means that the remote user's internet-bound traffic will not be forced through the corporate network but will be sent directly to the internet. This can improve performance and reduce latency for non-corporate internet traffic.
Extra explanation:
https://help.fortinet.com/fos50hlp/56/Content/FortiOS/fortigate-
sslvpn/SSLVPN_Examples/Split_Tunnel.htm#:~:text=Split%20Tunnel,SSL%20VPN%20on%20FortiGate
%20units.

RPF protect against IP spoofin attacks. The source IP address is checked against the routing table for a return path. RPF is only carried out on: The first packet in the session, not on reply.

Root VDOM is created by default when VDOMs are enabled.
configure on Fortigate:
- captive portal authentication required
- Authentication failed message for Sales users
- Authentication success for HR users
- second policy used by HR users
In FortiOS, when setting up a FortiGate in split VDOM mode, the default VDOMs created are FG-traffic and Root.
So, in this case, the correct answers would be A. FG-traffic and D. Root.

C because it exceeded the Extreme memory threshold.
"However, if the memory usage exceeds the extreme threshold, new sessions are ALWAYS DROPPED, regardless of the FortiGate configuration." if the memory usage keeps increasing, it might exceed the extreme threshold. While the memory usage is above this highest threshold, all new sessions are dropped.
Note: "Extreme threshold is when the memory usage goes above 95%, and all NEW sessions are dropped.

Automation stitches on FortiGate can have one or more triggers, which are conditions or events that activate the automation stitch. The trigger defines when the automation stitch should execute the defined actions.
Actions within a stitch can be executed sequentially or in parallel, depending on the configuration.
References:
* FortiOS 7.4.1 Administration Guide: Automation Stitches