Which component must be enabled and running on each host machine to achieve your objective?

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.
Enterprise Manager with Database Control

B.
Enterprise Manager with Generic Database Management

C.
Operating System Socket for incoming requests

D.
Enterprise Manager with Grid Control

E.
Oracle Management Agent

F.
Real Application Cluster (RAC) with three instances