A headless installation is an installation method that does not require a graphical user interface (GUI) or a monitor, keyboard, and mouse. It can be done remotely through a network connection or a command-line interface. A headless installation is suitable for a server that has limited resources and does not need a GUI.
References:
CompTIA Server+ Certification Exam Objectives1, page 14
Server Management: Server Hardware Installation and Management2, Module 2, Lesson 5

The most likely cause of the servers displaying the wrong time is A. A firewall. A firewall is a network security device that monitors and controls incoming and outgoing network traffic based on predefined rules. A firewall can block or allow certain ports, protocols, or applications that are used for network communication.
One of the protocols that is used for time synchronization is the Network Time Protocol (NTP), which requires the use of UDP port 123 for all time synchronization1. If a firewall blocks this port, it can prevent the servers from obtaining the correct time from the time source. Therefore, the server administrator should check the firewall settings and make sure that UDP port 123 is allowed for NTP traffic.

This is the best description of a synthetic full backup method because it creates a full backup by combining previous incremental backups with the latest backup. An incremental backup copies only the files that have changed since the last backup, while a full backup copies all the files. A synthetic full backup reduces the storage space and network bandwidth required for backups, while also simplifying the restore process by using a single file. References:
https://www.veritas.com/support/en_US/doc/129705091-129705095-0/br731_wxrt-tot_v131910378-129705095

A CMOS battery failure can cause the server to lose its BIOS settings, including the date and time, which can affect the server's functionality and connectivity. The servers have NTP (Network Time Protocol) configured to synchronize their clocks with a reliable time source, which can prevent time drift and ensure consistent timestamps. If one server has a wrong date and time, it can cause conflicts and errors with the other servers that have NTP configured.
References:
* CompTIA Server+ Certification Exam Objectives1, page 9
* Signs or symptoms of a CMOS battery failure2
* NTP: Network Time Protocol

Port 443 is the default port for HTTPS, which is the protocol used for secure web communication. HTTPS uses SSL/TLS certificates to encrypt the data between the web server and the browser. Port 443 is commonly used for web servers that need to provide secure services, such as online banking, e-commerce, or email. By allowing port 443, the administrator can access the web server's interface and manage its settings1.
Port 3389 is the default port for RDP, which is the protocol used for remote desktop connection. RDP allows a user to remotely access and control another computer over a network. Port 3389 is commonly used for remote administration, technical support, or remote work. By allowing port 3389, the administrator can connect to the web server's desktop and perform tasks that require graphical user interface2.