Which three statements are true about dropping and unused columns in an Oracle database?

[Reference: Oracle Database SQL Language Reference confirms that the DROP COLUMN operation is transactional and can be rolled back if it is not committed (Oracle Database SQL Language Reference, 12c Release 1 (12.1))., C. An UNUSED column's space is remained automatically when the block containing that column is next queried. (Incorrect), The space occupied by an UNUSED column is not automatically reclaimed in this way., D. An UNUSED column's space is remained automatically when the row containing that column is next queried. (Incorrect), Similar to C, the space for an UNUSED column is not reclaimed automatically upon querying the row., E. Partition key columns cannot be dropped. (Correct), Partition key columns are integral to the partitioning strategy of a table and cannot be dropped., Reference: Oracle Database VLDB and Partitioning Guide details the restrictions on dropping partition key columns (Oracle Database VLDB and Partitioning Guide, 12c Release 1 (12.1))., F. A column that is set to UNUSED still counts towards the limit of 1000 columns per table. (Correct), Marking a column as UNUSED is a logical operation that prevents it from being used in future DML operations, but it still counts towards the column limit of the table until it is actually dropped from the table., Reference: Oracle Database SQL Language Reference indicates that UNUSED columns count toward the column limit (Oracle Database SQL Language Reference, 12c Release 1 (12.1))., ]