For external tables in Oracle:
* C. DML statements cannot be used on them: External tables are read-only in Oracle. They allow access to data in external sources as if it were within a table in the database, but they do not support DML operations (INSERT, UPDATE, DELETE).
* D. Their data can be retrieved by using only SQL or PL/SQL: You can query the data in external tables using SQL or PL/SQL, just as you would with regular database tables.
Incorrect options are:
* A: You cannot create indexes directly on external tables.
* B: External tables cannot be populated using the CREATE TABLE AS SELECT command since they are primarily meant for accessing data stored outside the database.
* E: Only the metadata of an external tables is stored in the database; the actual data remains in external files.