Explanation:
The information that the database is now in ARCHIVE LOG mode stored is stored in the control file. Incorrect Answer:
1: This information is not stored in SPFILE.
2: Archive logs do not contain information about ARCHIVE LOG mode of the database.
4: This information is not stored in the SYSTEM table space.
Reference:
OCP Oracle 9i Database: Fundamentals II Exam Guide, Rama Velpuri, p. 187-189
Chapter 8: Configuring the Database Archive Mode

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