FTP (File Transfer Protocol) uses TCP ports 20/21 and transfers data in cleartext, which means the data is not encrypted and can be read by anyone who intercepts it. This makes FTP insecure for transferring sensitive information. SSH (Secure Shell), on the other hand, uses port 22 and encrypts data, making it more secure.
SNMP (Simple Network Management Protocol) uses ports 161/162 and is used to monitor network devices.
Telnet uses port 23 and transfers data in cleartext, making it insecure. References: CompTIA A+ Certification Exam: Core 1 - Page 199

Two-factor authentication (2FA) is a method of verifying a user's identity by requiring two pieces of evidence:
something the user knows (such as a password) and something the user has (such as a device). A mobile authenticator application is a software program that runs on a smartphone or tablet and generates a one-time code or token that the user can enter along with their password to access a system. This adds an extra layer of security to prevent unauthorized access.
References
*The Official CompTIA A+ Core 1 Student Guide (Exam 220-1101), page 13-14
*CompTIA A+ Certification Exam Core 1 Objectives, page 9, objective 2.5
*What is Two-Factor Authentication?

The shared-tenant model for a cloud deployment, also known as a multi-tenant model, allows multiple customers to use the same resources and infrastructure of the cloud service provider, with each customer's data and applications isolated from one another. This model is often chosen for cost savings, as resources are shared and users only pay for what they use. Therefore, the MOST likely reason that an administrator chose this model is A. Cost savings.

The message stating that one or more disks are in a degraded state is a clear indication of a RAID failure.
RAID stands for Redundant Array of Independent Disks, and it is a technology used to provide fault tolerance and improve performance by combining multiple hard drives into a single logical unit.
The message indicating that the OS is missing is most likely caused by a bootable device not found. This means that the server is unable to boot from the designated boot device, which could be the hard drive, a CD/DVD drive, or a USB flash drive. This could be caused by a faulty boot device, a loose cable, or a misconfiguration in the BIOS or UEFI settings.