Explanation: A: Occasionally a database closes abnormally with one or more distributed transactions in doubt (neither committed nor rolled back). When you reopen the database and recovery is complete, the RECO background process automatically, immediately, and consistently resolves any in-doubt distributed transactions. C: Crash and instance recovery involve two distinct operations: rolling forward the current, online datafiles by applying both committed and uncommitted transactions contained in online redo records, and then rolling back changes made in uncommitted transactions to their original state. D: The SMON background process performs instance recovery, applying online redo automatically. No user intervention is required. References: https://docs.oracle.com/cd/B28359_01/server.111/b28318/startup.htm https://docs.oracle.com/database/121/CNCPT/startup.htm