What is the most cost effective way to update firmware in each location?

Company servers are in the branch offices located at different geographic locations. All servers are running ESXi hypervisor. The are no network connections between the branch office and central office.

What is the most cost effective way to update firmware in each location?
A . Send a server administrator on site to update firmware using iDRAC/LC
B . Export DUP scripts from Repository Manager to a USB key and ship to each location.
C . Export a bootable ISO from Repository Manager and ship to each location.
D . Use OpenManage Essentials to push updates to each location.

Answer: D