This is the most likely licensing type that will be used because volume licensing allows a single license key to be used for multiple installations of a software product. Volume licensing is typically used by organizations that need to deploy software to a large number of devices or users. References:
https://www.microsoft.com/en-us/licensing/licensing-programs/volume-licensing-programs

The subnet mask is most likely containing an error that prevents the application server from communicating with the newly installed database server. The subnet mask is a binary number that defines how many bits of an IP address are used for the network portion and how many bits are used for the host portion. The subnet mask determines which devices belong to the same network or subnet and can communicate directly with each other without routing or switching devices. The subnet mask of the database server is 255.255.O.O, which means that all 32 bits of its IP address are used for the network portion and none for the host portion, which is invalid and makes it unreachable by any other device on any network or subnet. The subnet mask of the application server is 255.O.O.O, which means that only 8 bits of its IP address are used for the network portion and 24 bits are used for the host portion, which is also uncommon and makes it incompatible with most networks or subnets. Reference: [CompTIA Server+ Certification Exam Objectives], Domain 4.0: Networking, Objective 4.1: Given a scenario, configure network settings for servers.

Explanation
Phishing is a type of attack that is the most difficult to mitigate with technology. Phishing is a technique of deceiving users into revealing their personal or confidential information, such as passwords, credit card numbers, or bank accounts, by sending them fraudulent emails or messages that appear to be from legitimate sources. Phishing relies on human factors, such as curiosity, greed, or fear, to trick users into clicking on malicious links or attachments, or entering their credentials on fake websites. Technology solutions, such as antivirus software, firewalls, or spam filters, can help detect and block some phishing attempts, but they cannot prevent users from falling victim to social engineering tactics. References: [CompTIA Server+ Certification Exam Objectives], Domain 5.0: Security, Objective 5.3: Given a scenario, explain methods and techniques to secure data.

Explanation
A backdoor is a security risk that provides unauthorized access to an application. A backdoor is a hidden or undocumented way of bypassing the normal authentication or encryption mechanisms of an application, allowing an attacker to gain remote access, execute commands, or steal data. A backdoor can be created intentionally by the developer, maliciously by an attacker, or unintentionally by a programming error. References: CompTIA Server+ Certification Exam Objectives, Domain 5.0: Security, Objective 5.2:
Given a scenario, apply logical access control methods.