Which create table statement is valid?

Which create table statement is valid?

A.
Option A

B.
Option B

C.
Option C

D.
Option D

Explanation:
PRIMARY KEY Constraint
A PRIMARY KEY constraint creates a primary key for the table. Only one primary key can
be created for each table. The PRIMARY KEY constraint is a column or a set of columns
that uniquely identifies each row in a table. This constraint enforces the uniqueness of the
column or column combination and ensures that no column that is part of the primary key
can contain a null value.
Note: Because uniqueness is part of the primary key constraint definition, the Oracle server
enforces the uniqueness by implicitly creating a unique index on the primary key column or
columns.