Which three are true about dropping columns from a table? (Choose three.)

[answerhappygod]

Which three are true about dropping columns from a table? (Choose three.)

A. A column must be set as unused before it is dropped from a table.
B. A primary key column cannot be dropped.
C. Multiple columns can be dropped simultaneously using the ALTER TABLE command.
D. A column can be removed only if it contains no data. E. A column that is referenced by another column in any other table cannot be dropped. F. A column drop is implicitly committed.