Explanation
The most likely cause of the issue is C. Misconfiguration in the network ACL. A network ACL (access control list) is a set of rules that controls the inbound and outbound traffic for a subnet or a virtual network in a cloud environment. A misconfiguration in the network ACL can block the communication between the web application and the managed database, resulting in data loss or unavailability. For example, according to the Azure SQL Database documentation1, if you use a virtual network service endpoint to secure your database, you need to configure the network ACL to allow traffic from the web application subnet to the database subnet. Otherwise, the web application will not be able to connect to the database. Similarly, according to the DigitalOcean tutorial2, if you use a managed database cluster, you need to add the web application's IP address or Droplet to the cluster's trusted sources list. Otherwise, the web application will not be able to access the database.
A misconfiguration in the user permissions, the routing traffic, or the firewall can also cause connectivity issues between the web application and the managed database, but they are less likely than a misconfiguration in the network ACL. A misconfiguration in the user permissions can prevent the web application from authenticating or authorizing with the database, but it will not affect the data transmission. A misconfiguration in the routing traffic can cause packets to be lost or delayed, but it will not block the communication entirely.
A misconfiguration in the firewall can filter out unwanted traffic, but it will not affect the traffic that is allowed by the network ACL. Therefore, these are not the most likely causes of the issue. For more information on how to troubleshoot connectivity issues between a cloud-hosted web application and a managed database, you can refer to the AWS documentation3 or the Google Cloud documentation.

Explanation
A storage live migration is a process of moving or transferring data or files from one storage system or device to another without interrupting or affecting the availability or performance of the VMs or applications that use them. Performing a storage live migration can help migrate the data from a SAN that is being decommissioned to a new array, as it can ensure that there is no downtime or disruption for the VMs or applications that rely on the data or files stored on the SAN. Performing a storage live migration can also help maintain consistency and integrity, as it can synchronize and verify the data or files between the source and destination storage systems or devices. References: CompTIA Cloud+ Certification Exam Objectives, page 10, section 1.5

Explanation
According to the CompTIA Cloud+ Study Guide1, scaling is "the ability to increase or decrease the size or capacity of a cloud service". There are two main types of scaling: horizontal and vertical.
Horizontal scaling is "the ability to increase or decrease the number of instances or nodes of a cloud service".
This means that horizontal scaling can add or remove servers or virtual machines to a cloud service, depending on the workload demand. Horizontal scaling can improve availability, reliability, and performance, but it can also increase complexity and cost.
Vertical scaling is "the ability to increase or decrease the resources allocated to an instance or node of a cloud service". This means that vertical scaling can add or remove CPU, memory, disk, or network resources to a server or virtual machine, depending on the workload demand. Vertical scaling can improve performance and efficiency, but it can also have limitations and risks.
Cloud bursting is "a technique that allows a private cloud to use public cloud resources when it reaches its capacity limit". This means that cloud bursting can extend the private cloud to the public cloud when there is a peak in demand that exceeds the private cloud resources. Cloud bursting can provide scalability, flexibility, and cost savings, but it can also introduce challenges such as security, compatibility, and latency.
Autoscaling is "the ability to automatically increase or decrease the number of resources allocated to a cloud service based on the current demand". This means that autoscaling can adjust the size or capacity of a cloud service without human intervention, using predefined rules or policies. Autoscaling can optimize performance, availability, and cost, but it can also require careful monitoring and configuration.
Based on this information, I think the best answer to your question is C. Cloud bursting. Cloud bursting can help the company utilize its private cloud for the new application and also access public cloud resources when the private cloud resources can only meet 75% of the application's requirements. This way, the company can accommodate 100% of the application's requirements without having to purchase extra computing resources for their private cloud.
I hope this helps you understand the concept of cloud bursting better. If you want to learn more about CompTIA Cloud+, you can check out some of these resources:
CompTIA Cloud+ : Cloud High Availability & Scaling: A video course that covers the topics of high availability and scaling in cloud environments, including autoscaling, horizontal scaling, vertical scaling and cloud bursting.
Cloud+ (Plus) Certification | CompTIA IT Certifications: The official website of CompTIA Cloud+, where you can find exam details, preparation materials, renewal information and more.

Explanation
The wrong template selection is the most likely cause of the issue of newly provisioned Linux VMs running an earlier version of OS than they should be in a private IaaS environment. A template is a preconfigured image or blueprint of a VM that contains an OS, applications, settings, etc., that can be used to create new VMs quickly and consistently. A template may have different versions or updates depending on when it was created or modified. If a template is selected incorrectly or not updated properly, it may result in creating VMs with an older or different version of OS than expected.