A: True, the name of a column can be changed in Oracle using the ALTER TABLE ... RENAME COLUMN command.
B: False, you cannot change a column's data type from NUMBER to VARCHAR2 if the table contains data, unless the change does not result in data loss or inconsistency.
C: True, it is possible to change a DATE data type column to TIMESTAMP because TIMESTAMP is an extension of DATE that includes fractional seconds. This operation is allowed if there is no data loss.
D: False, any column that is not part of a primary key or does not have a non-deferrable constraint can generally be dropped unless it contains data that does not allow for such a change.
E: False, the DEFAULT clause can be added to a column provided there is no data that contradicts the default value or it doesn't violate any constraints.
These statements are verified against the Oracle Database 12c SQL documentation, specifically the sections on data types, the ALTER TABLE command, and the use of literals in SQL expressions.