Which VMware Tools upgrade method minimizes the need for scheduled downtime?

Which VMware Tools upgrade method minimizes the need for scheduled downtime?

A.
Use vCenter Server to select and upgrade virtual machines

B.
Use vSphere PowerCLI and create a script to upgrade the virtual machines

C.
Use Update Manager to perform an orchestrated upgrade of virtual machines

D.
Configure the virtual machines to check for and install updates at each reboot cycle