Which of the following queries is valid?

a. SELECT b.title, b.retail, o.quantity

FROM books b NATURAL JOIN orders od

NATURAL JOIN orderitems o

WHERE od.order# = 1005;

b. SELECT b.title, b.retail, o.quantity

FROM books b, orders od, orderitems o

WHERE orders.order# = orderitems.order#

AND orderitems.isbn = books.isbn

AND od.order# = 1005;

c. SELECT b.title, b.retail, o.quantity

FROM books b, orderitems o

WHERE o.isbn = b.isbn

AND o.order# = 1005;

d. None of the above