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.