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 site 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.
RPRR and SSO

C.
SSO only

D.
RPR only