Prism Element is a management interface that allows administrators to assign permissions to users and groups on a per-cluster, per-VM, or per-storage container basis.
https://www.nutanix.com/content/dam/nutanix/resources/support/ncp-mci-ds.pdf

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.

According to the Nutanix Support & Insights web search result3, shadow clones are vDisk copies that are created by the cluster when a vDisk is read by multiple VMs. Shadow clones are immutable copies of a vDisk that are stored in different nodes in the cluster, and are used to improve read performance and reduce network traffic. Shadow clones are automatically created and deleted by the cluster, based on the demand and availability of resources.

Enable Memory Overcommit on the over-provisioned VMs is the most efficient resolution to enable additional VMs to be created. Memory overcommit allows VMs to use more memory than physically available on a host by compressing and swapping memory pages to storage1. This can improve memory utilization and increase VM density on a cluster1. However, memory overcommit is not supported when HA is configured to use reserved hosts, so you may need to disable HA reservation on the cluster before enabling memory overcommit
1.