Which statement is true regarding Oracle Net connectivity for a Data Guard Broker configuration? 

Answer options:

A. To start SQL apply on a logical standby database, a TNS entry enabling connectivity to the primary database instance must be defined on the logical standby database host.
B. the LOCAL_LISTERNER initialization parameter must be set to the listener used to register the primary database instance.
C. To enable Real_Time Query on a physical standby database, a TNS entry enabling connectivity to the standby database instance must be defined on the primary database host.
D. A TNS enabling connectivity to the primary database instance must be defined on each of the standby database hosts.
E. A TNS entry or entries enabling connectivity to standby database instance(s) must be defined on the primary database host.

D

The tnsnames.ora on both Primary as well as Standby sites have entries for the databases. Note: TNSNAMES.ORA is a SQL*Net configuration file that defines databases addresses for establishing connections to them. References: http://gavinsoorma.com/2013/08/minimal-downtime-rolling-database-upgrade-to-12c-release-1/