A: This statement is false. A table can only have one primary key, although the primary key can consist of multiple columns (composite key).
B: This statement is true. A table can have multiple foreign keys referencing the primary keys of other tables or the same table.
C: This statement is false. A NUMBER column without data is NULL, not zero.
D: This statement is false. A column definition must specify exactly one data type.
E: This statement is true. A VARCHAR2 column without data defaults to NULL, not an empty string.