How can they ensure that customized fields or Supplemental Emissions are not changed when they update Net Zero Cloud with a new release?

A Sustainability Manager wants to update the Net Zero Cloud package.

How can they ensure that customized fields or Supplemental Emissions are not changed when they update Net Zero Cloud with a new release? (1)
A . The managed package will automatically deploy with each release and maintain custom fields
B. Upgrade via the Partner who originally installed the package who will manage the custom fields
C. A managed package can be deployed manually when the customer is ready and will maintain custom fields
D. Nothing needs to be done because Net Zero Cloud updates automatically three times per year

Answer: C