What is the best upgrade method when the management server is not connected to the Internet?

Customer’s R80 management server needs to be upgraded to R80.10.

What is the best upgrade method when the management server is not connected to the Internet?
A . Export R80 configuration, clean install R80.10 and import the configuration
B . CPUSE online upgrade
C . CPUSE offline upgrade
D . SmartUpdate upgrade

Answer: C