ocp 19c考题，科目082考试题(16)-about dropping and unused columns

16.Which three statements are true about dropping and unused columns in an Oracle database?(Choose three.)A. A primary key column referenced by another column as a foreign key can be dropped if using the CASCADE option.B. An UNUSED column’s space is reclaimed automatically when the block containing that column is next queried.C. An UNUSED column’s space is reclaimed automatically when the row containing that column is next queried.D. Partition key columns cannot be dropped.E. A DROP COLUMN command can be rolled backF. A column that is set to UNUSED still counts towards the limit of 1000 columns per tablesource : cuug