Explanation
Changing the boot order on the server and restricting console access would prevent unauthorized access attempts via USB devices at startup, as the server would not boot from any external media and only authorized users could access the console. Setting a BIOS/UEFI password on the server would also help, but it could be bypassed by resetting the CMOS battery or using a backdoor password. Configuring the host OS to deny login attempts via USB would not prevent booting from a malicious USB device that could compromise the system before the OS loads. Disabling all the USB ports on the server would limit functionality, as some peripherals or devices may need to use them. References:
https://www.pcmag.com/how-to/dont-plug-it-in-how-to-prevent-a-usb-attack
https://www.techopedia.com/definition/10362/boot-order
https://www.techopedia.com/definition/10361/console-access
https://www.techopedia.com/definition/102/bios-password
https://www.techopedia.com/definition/10363/cmos-battery

Since this is legacy server hardware it would be important to make sure that it can handle/support a particular O/S before attempting an install. The rest of the answers have little to nothing to do with an install an O/S on legacy hardware.

Comprehensive Detailed Explanation with all CompTIA Server+ SK0-005 Study Guide References:
When troubleshooting server access issues, identifying recent changes to the environment is critical. Changes such as updates, patches, configuration modifications, or network adjustments could be the root cause of the issue. This aligns with the best practices of the ITIL framework and troubleshooting methodologies outlined in the CompTIA Server+ study materials:
* Step 1: Gather information and identify the scope of the problem.
* Step 2: Look for recent changes to identify potential triggers.This approach ensures that corrective actions are based on an understanding of what caused the problem, avoiding unnecessary disruptions or incorrect fixes.

The hosts file is a file that maps hostnames to IP addresses on a server or a computer. It can be used to override or supplement the DNS (Domain Name System) resolution for certain hosts or domains. If the hosts file is misconfigured, it may return a different IP address for a hostname than the one registered in the DNS server, causing connectivity issues or errors. Verified Reference: [Hosts file], [DNS]

The correct answer is D. per-core.
The per-core licensing model was created by software companies in response to the increasing density of processors. This model is used for software that runs on servers with multi-core processors, and the licensing fee is based on the number of cores. This way, the software vendors can charge more for software that runs on servers with more processing power1