Question on UNUSED Columns

[Vipassana]

Could someone please answer this Q for me?

Many Thanks,
Vipassana

ABC Company consolidated into one office building, so the very large EMPLOYEES table no longer requires the OFFICE_LOCATION column. The DBA decided to drop the column using the syntax below:
ALTER TABLE hr.employees
DROP COLUMN building_location
CASCADE CONSTRAINTS;
Dropping this column has turned out to be very time consuming and is requiring a large amount of undo space.
What could the DBA have done to minimize the problem regarding time and undo space consumption?
A. Use the Export and Import utilities to bypass undo.
B. Mark the column as UNUSED.
C. Remove the column at a later time when less activity is on the system.
D. Drop all indexes and constraints associated with the column prior to dropping the column.
E. Mark the column INVALID prior to beginning the drop to bypass undo.
F. Remove the column using the DROP UNUSED COLUMNS command.

[pando]

RTFM

[mrchrispy]

I'll tell you what, you paint my house and I'll answer your exam questions