The backup type that only records changes to the data blocks on a virtual machine is snapshot. A snapshot is a point-in-time copy of a virtual machine (VM) that captures the state and data of the VM at a specific moment.
A snapshot can be created instantly and with minimal overhead, as it only stores the changes made to the VM after the snapshot was taken. A snapshot can be used to restore the VM to its previous state in case of data loss or corruption.

The technician should install the Type 1 hypervisor on a SAS drive. A Type 1 hypervisor is a layer of software that runs directly on top of the physical hardware and creates virtual machines that share the hardware resources. A Type 1 hypervisor requires fast and reliable storage for optimal performance and stability. A SAS drive is a type of hard disk drive that uses Serial Attached SCSI (SAS) as its interface protocol. SAS drives offer high speed, low latency, and high reliability compared to other types of drives, such as SD cards, NAS drives, or SATA drives. SD cards are flash memory cards that offer low cost and portability but have low speed, low capacity, and low durability. NAS drives are network-attached storage devices that offer high capacity and easy access but have high latency and low reliability due to network dependency. SATA drives are hard disk drives that use Serial ATA (SATA) as their interface protocol. SATA drives offer moderate speed, moderate cost, and moderate reliability but have lower performance and durability than SAS drives.

If a server has three hard drives configured in a RAID 5 array, it means that the data is striped across all three drives with parity information. RAID 5 can tolerate one drive failure without losing data, but not two or more. If there are multiple failed hard drives, the RAID 5 array will become corrupted and the OS will not load. The other options are not likely to cause the issue, as the server passes POST, the CPU and RAM are seated correctly, the BIOS settings are correct, and the OS loads from a bootable USB drive. RAID 5 does not require four drives, it can work with three or more. Reference: https://www.technewstoday.com/what-is-a-raid-5/

An action that the administrator should take to harden the hardware of a new server is to set a BIOS password.
BIOS (Basic Input/Output System) is a firmware that initializes the hardware components and settings of a system before loading the operating system. BIOS password is a security feature that requires a user to enter a password before accessing or modifying the BIOS settings or booting up the system. By setting a BIOS password, the administrator can prevent unauthorized or malicious users from changing the hardware configuration or boot order of the server.
References: CompTIA Server+ SK0-005 Certification Study Guide, Chapter 5, Lesson 5.1, Objective 5.1