C is correct. Security check option.
For context, Host Check uses the FortiClient to check that certain conditions on the remote PC are met, such as having AV installed, that there is a specific file located on the PC, that a certain process is running on the PC, or that specific registry entries exist on the PC. Host Check basically ensures that the PC with the VPN Client installed is setup according to your organizations standards.
When implementing two-factor authentication for SSL VPN access, configuring a host check is an additional best practice. A host check involves checking the security posture and compliance of the connecting device before granting access. This can include checking for the presence of antivirus software, ensuring that the device is up-to-date with patches, and verifying other security-related configurations.
This additional layer of security helps ensure that the devices connecting to the SSL VPN meet certain security requirements, reducing the risk of compromised devices gaining access to the network. It adds an extra level of assurance that the connecting devices are not only authenticating through two factors (such as username/password and a token) but also adhering to security policies.