Which of the following statements is valid? a. SELECT title FROM books WHERE retail WHERE isbn = ' XXXXXXXXXX'); b. SELECT title FROM books WHERE retail = (SELECT cost FROM books WHERE isbn =...

Which of the following statements is valid?

a. SELECT title FROM books

WHERE retail<(select>

WHERE isbn = '9959789321');

b. SELECT title FROM books

WHERE retail = (SELECT cost FROM books

WHERE isbn = '9959789321' ORDER BY cost);

c. SELECT title FROM books

WHERE category IN (SELECT cost FROM orderitems

WHERE isbn = '9959789321');

d. none of the above statements