Explanation:
You can drop the tablespace and the segments, and also delete the OS datafiles with the following command: DROP TABLESPACE tablespace_name INCLUDING CONTENTS and DATAFILES.
Incorrect Answers:
1: You cannot achieve this purpose with the DROP DATAFILE command.
3: You can delete not-OMF datafiles also using the DROP TABLESPACE command.
4: To delete not-OMF datafiles you don’t need to be ensure that the DB_FILE_CREATE_DEST initialization parameter is set before using the DROP TABLESPACE command.
Reference:
OCP Oracle9i Database: New Features for Administrators, Daniel Benjamin, p. 157-158
Chapter 3: Manageability Enhancements
Oracle 9i New Features, Robert Freeman, p. 2-12
Chapter 1: Oracle9i Database Administration and Management Features

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