You have three databases， FINDB， PAYDB and ADMINDB， located in Sydney， Tokyo and Singapore respectively. You want to perform administrative tasks which include starting up and shutting down the databases， creating and managing tablespaces and database users， and taking regular backups， for all of the three databases from London. Which component must be enabled and running on each host machine to achieve your objective？（）

A. Oracle Management Agent

B. Enterprise Manager with Grid Control

C. Enterprise Manager with Database Control

D. Operating System Socket for incoming requests

E. Real Application Cluster （RAC） with three instances

F. Enterprise Manager with Generic Database Management