Note the functionalities of various background processes：  1：Perform recovery at instance startup. SMON  2：Free the resources used by a user process when it fails. PMON  3：Cleanup the database buffer cache when a process fails. PMON  4：Dynamically register database services with listeners. PMON  5：Monitor sessions for idle session timeout. PMON  6：Cleanup unused temporary segments. SMON  7：Record the checkpoint information in control file. CKPT  Which option has the correct functionalities listed for a background process（）

• A、Checkpoint （CKPT）： 1， 2， 5
• B、System Monitor （SMON）： 1， 6
• C、Process Monitor （PMON）： 4， 6， 7
• D、Database Writer （DBWR）： 1， 3， 4