Which procedure is used as the last resort disaster recovery procedure to completely replace the
currently installed IOS XR software on Cisco IOS XR routers?

A.
netboot

B.
turboboot

C.
install recovery

D.
install rollback

E.
install add and install activate

Explanation:
http://www.cisco.com/en/US/docs/routers/crs/software/crs_r4.0/migration/guide/tbupgapp.pdf