According to the exhibit, the wireless guest users are getting a certificate error while loading the captive portal login page. This means that the browser cannot verify the identity of the server that is hosting the login page.
Therefore, option A is true because the external server FQDN is incorrect, which means that it does not match the common name or subject alternative name of the server certificate. Option B is also true because the wireless user's browser is missing a CA certificate, which means that it does not have the root or intermediate certificate that issued the server certificate. Option C is false because the FortiGate authentication interface address is using HTTPS, which is a secure protocol that encrypts the communication between the browser and the server. Option D is false because the user address is not in DDNS form, which is not related to the certificate error.