Explanation:
Oracle9i overcomes the problem of rebuilding the global index by giving you the option to update global indexes as Oracle performs the partition DDL. This feature is not applicable to local indexes, domain indexes, index-organized tables (IOTs), or to indexes that were UNUSABLE prior to start of the partition DML. You can invoke this capability by using the optional clause UPDATE GLOBAL INDEX of the ALTER TABLE command. You can use this clause with the ADD, COALESCE, DROP, EXCHANGE, MERGE, MOVE, SPLIT, and TRUNCATE partition DDL commands.
Incorrect Answers:
2: Nonpartitioned indexes on the SALES table will not be marked UNUSABLE.
3: All valid global indexes on the SALES table will retain their USABLE status after the statement completes.
4: Global indexes on the SALES table will be maintained concurrently with the exchange operation disregarding if the statement executes with the desired degree of parallelism.
Reference:
OCP Oracle9i Database: New Features for Administrators, Daniel Benjamin, p. 130-131
Chapter 3: Manageability Enhancements
Oracle 9i New Features, Robert Freeman, p. 102-107
Chapter 4: New Oracle9i Database DDS and Data-Warehouse Features

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