When multicast-skip-policy is enabled, no check is performed based on multicast policy. A multicast packet received on an interface is flooded unconditionally to all interfaces (except the incoming interface) belonging to the same forwarding domain. Multicast packets are forwarded even when there is no multicast policy or the multicast policy is set to deny. To forward multicast traffic based on multicast policy, multicast-skip-policy must be disabled. In transparent mode, there is a per-VDOM configuration to skip policy check and forward all multicast traffic. This command is only available in transparent mode, and is disabled by default.

When using inbound SSL inspection, FortiGate needs to present a certificate to the client that matches the requested domain name. If no matching certificate is found in the server-cert list, FortiGate will fall-back to the default Fortinet_CA_SSL certificate, which is self-signed and may trigger a warning on the client browser. Reference: https://docs.fortinet.com/document/fortigate/6.4.0/cookbook/103437/inbound-ssl-inspection

The fabric-object-unification setting on FGT_2 is set to local, which means that objects will not be synchronized to any other FortiGate devices in the security fabric. The default setting for fabric-object-unification is default, which means that objects will be synchronized from the root FortiGate to all downstream FortiGate devices.
Since FGT_2 is not the root FortiGate and the fabric-object-unification setting is set to local, objects from the root FortiGate will not be synchronized to FGT_2.
Reference:
Synchronizing objects across the Security Fabric: https://docs.fortinet.com/document/fortigate/6.4.0/administration-guide/880913/synchronizing-objects-across-the-security-fabric

D is correct because Spoke1 will establish an ADVPN shortcut to Spoke2 when it detects that there is a demand for traffic between them. This is explained in the Fortinet Community article on Technical Tip:
Fortinet Auto Discovery VPN (ADVPN) under Summary - ADVPN sequence of events. References:
https://community.fortinet.com/t5/FortiGate/Technical-Tip-Fortinet-Auto-Discovery-VPN-ADVPN/ta-p
/195698

The customer wants to deploy a solution to authenticate the clients connected to a hardware switch interface of a FortiGate 400E device. A hardware switch interface is an interface that combines multiple physical interfaces into one logical interface, allowing them to act as a single switch with one IP address and one set of security policies. The customer wants to use 802.1X authentication for this solution, which is a standard protocol for port-based network access control (PNAC) that authenticates clients based on their credentials before granting them access to network resources. One condition that allows authentication to the client devices before assigning an IP address is that devices connected directly to ports 3 and 4 can perform 802.1X authentication. This is because ports 3 and 4 are part of the hardware switch interface named "lan", which has an IP address of 10.10.10.254/24 and an inbound SSL inspection profile named "ssl-inspection". The inbound SSL inspection profile enables the FortiGate device to intercept and inspect SSL/TLS traffic from clients before forwarding it to servers, which allows it to apply security policies and features such as antivirus, web filtering, application control, etc. However, before performing SSL inspection, the FortiGate device needs to authenticate the clients using 802.1X authentication, which requires the clients to send their credentials (such as username and password) to the FortiGate device over a secure EAP (Extensible Authentication Protocol) channel. The FortiGate device then verifies the credentials with an authentication server (such as RADIUS or LDAP) and grants or denies access to the clients based on the authentication result. Therefore, devices connected directly to ports 3 and 4 can perform 802.1X authentication before assigning an IP address. Another condition that allows authentication to the client devices before assigning an IP address is that client devices must have 802.1X authentication enabled. This is because 802.1X authentication is a mutual process that requires both the client devices and the FortiGate device to support and enable it. The client devices must have 802.1X authentication enabled in their network settings, which allows them to initiate the authentication process when they connect to the hardware switch interface of the FortiGate device. The client devices must also have an 802.1X supplicant software installed, which is a program that runs on the client devices and handles the communication with the FortiGate device using EAP messages. The client devices must also have a trusted certificate installed, which is used to verify the identity of the FortiGate device and establish a secure EAP channel. Therefore, client devices must have 802.1X authentication enabled before assigning an IP address. References: https://docs.fortinet.com/document/fortigate/7.0.0/administration-guide/19662/hardware-switch-interfaces https://docs.fortinet.com/document/fortigate/7.0.0/administration-guide/19662/802-1x-authentication