Explanation:
The main effect of activating a standby database is that the standby database becomes the primary database.
Incorrect Answers:
1: Old primary database can be used as standby database for new primary database after that, but this is not mandatory.
3: The primary database still can be active and used as standby database, for example.
4: After switchover between the primary and the standby database no more redo log files can be applied to the standby database, because of it's already the primary database and all redo logs for it have been reset.
Oracle 8, DBA Certification Exam Guide, Jason S. Couchman, p. 1159
Chapter 24: Oracle8i New Features Topics

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