The correct answer is D. Fewer than 30 I/Os and less than 1000 bytes per day of network traffic for the past 21 days.
A zombie VM is a type of inactive VM that is powered on but does very little activity. A zombie VM wastes host resources such as CPU, memory, disk, and network that could be used by other VMs. A zombie VM can be identified by using the VM Profile feature in Prism Central. The VM Profile feature analyzes the resource utilization of each VM and assigns it a profile based on its efficiency and impact on other VMs. The profiles are as follows1:
Efficient: The VM is well-provisioned and has optimal resource utilization.
Over-provisioned: The VM has more resources than it needs and has low resource utilization.
Constrained: The VM has less resources than it needs and has high resource utilization.
Inactive: The VM has no resource utilization and is idle or powered off.
Bully: The VM has high resource utilization and causes contention for other VMs.
A zombie VM is a subtype of an inactive VM that meets the following criteria2:
The VM is powered on for the past 21 days.
The VM does fewer than 30 read or write I/Os (total) per day for the past 21 days.
The VM receives or transfers fewer than 1000 bytes per day of network traffic for the past 21 days.
To identify a zombie VM, the administrator can use Prism Central to view the VM Profile dashboard and filter by profile type. The dashboard shows the number of VMs in each profile type, as well as their resource consumption and efficiency score. The administrator can also drill down into each VM to see its detailed metrics and recommendations for optimization.

According to the web search results, the most efficient action an administrator should take to ensure a supported state when adding a node with a higher AOS release to an existing cluster is to perform a standalone reimage of the new node and then add it to the cluster1. This way, the new node will have the same AOS version as the existing nodes, and there will be no compatibility issues or downtime. Therefore, option C is correct, while options A, B, and D are not.

The best way to fix this issue is to increase the amount of memory assigned to the VM from the Prism web console. This option allows the administrator to modify the VM configuration without accessing the CVM or shutting down the VM. The Prism web console provides a simple and intuitive interface for managing Nutanix clusters and VMs1. To change the memory allocation for a VM, the administrator can follow these steps2:
Go to the VM dashboard
Select the VM from the VMs list
Choose Update
Adjust the amount of memory assigned to the VM
Click Save

According to the Dell Unity: Data Reduction Technical White Paper1, snapshots and clones on Dell Unity use the Copy-on-Write (CoW) algorithm to maximize efficiency and effectiveness. CoW is a technique that defers the copying of data until it is modified. This means that snapshots and clones only consume space when changes are made to the source or the clone, respectively. CoW also preserves the original data in case of a rollback or recovery operation.