Given the following query:

SELECT zip, order#

FROM customers NATURAL JOIN orders;

Which of the following queries is equivalent?

a. SELECT zip, order#

FROM customers JOIN orders

WHERE customers.customer# = orders.customer#;

b. SELECT zip, order#

FROM customers, orders

WHERE customers.customer# = orders.customer#;

c. SELECT zip, order#

FROM customers, orders

WHERE customers.customer# = orders.customer# (+);

d. None of the above