com is deploying a new version of Cisco IOS Which supervisor Redundancy mode or modes will allow an older version of Cisco IOS to be maintained on a standby supervisor?

YourDomain.com site is set up as follows:
Aggregation-layer Cisco Catalyst 6500 Series Switches Redundant Supervisors
YourDomain.com is deploying a new version of Cisco IOS Which supervisor Redundancy mode or modes will allow an older version of Cisco IOS to be maintained on a standby supervisor?

A.
RPR and RPR+

B.
RPR only

C.
SSO only

D.
RPR and SSO