Explanation/Reference:
If STANDBY_MAX_DATA_DELAY is set to 0, a query issued to a physical standby database is guaranteed to return the exact same result as if the query were issued on the primary database, unless the standby database is lagging behind the primary database, in which case an ORA-3172 error is returned.
Real-time Query Restrictions include:
The standby database must receive redo data via the SYNC transport.
Note: In an Active Data Guard environment, this session parameter can be used to specify a session- specific apply lag tolerance, measured in seconds, for queries issued by non-administrative users to a physical standby database that is in real-time query mode.
Incorrect Answers:
C, D: Maximum Protection mode ensures that zero data loss occurs if a primary database fails.
Because this data protection mode prioritizes data protection over primary database availability, Oracle recommends that a minimum of two standby databases be used to protect a primary database that runs in maximum protection mode to prevent a single standby database failure from causing the primary database to shut down.
E: Should use STANDBY_MAX_DATA_DELAY parameter set to zero.
References: https://docs.oracle.com/cd/B28359_01/server.111/b28294/protection.htm
https://chenguangblog.wordpress.com/tag/standby_max_data_delay/