Explanation:
The key feature of a decision support system is fast sequential access to large amounts of data, so DSS environment prefer a large database block size. Also remember that you can reduce the number of block visits by packing rows as closely as possible into blocks, so Oracle will need less table scans to retrieve all needed blocks.
Incorrect Answers:

1: Random access to large objects will work better with small block size. It happens often in OLTP systems. For full scans large block size is more preferable (DSS systems).
2: Small block sizes will not result in more block contention.
5: So change the database block size, you must rebuild database. Shutdown the instance and STARTUP with RESETLOGS option will not change database block size.
Oracle 8, DBA Certification Exam Guide, Jason S. Couchman, p. 793-796. Chapter 17: Tuning Database Applications

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