An  administrator  runs  mktcpip  aixhost  172.168.0.50  enO  to  change  the  network  address，  but  the  command  hangs  for  an  extended  period  of  time.   Which  of  the  following  is  the  most  likely  cause  of  the  problem（）

• A、entO is in a defined state
• B、enO is currently active
• C、There is no physical network adapter on the system
• D、The address 172.168.0.50 is in use by another system