Which virtual machine file type should an administrator select to copy a single hard disk from one datastore to another?

When copying a single hard disk from one datastore to another in a VMware environment, the appropriate file type to select is the vmdk file. The vmdk, or Virtual Machine Disk, file contains the disk image for a virtual machine, which includes all the data on that virtual disk. It is essential for the virtual machine's operation and represents the actual storage structure that the virtual machine uses.

The other file types serve different purposes:

• The vmss file is associated with suspended virtual machines, containing the state of a VM when it is suspended.

• The vswp file is a swap file created during the operation of a virtual machine, utilized for memory management when the VM's physical memory is exhausted.

• The vmx file is the configuration file for a virtual machine, storing settings and specifications, but does not include the hard disk data.

Thus, selecting the vmdk file ensures that the entire data structure of the virtual disk is captured and can be effectively copied to another datastore.