Which of the following statements is correct? a. A PRIMARY KEY constraint allows NULL values in the

Question:

Which of the following statements is correct?
a. A PRIMARY KEY constraint allows NULL values in the primary key column(s).
b. You can enable a dropped constraint if you need it in the future.
c. Every table must have at least one PRIMARY KEY constraint, or Oracle 12c doesn’t allow the table to be created.
d. None of the above statements is correct.