Which of the following queries identifies other customers who were referred to JustLee Books by the same person who referred Jorge Perez?
a. SELECT customer# FROM customers

WHERE referred = (SELECT referred FROM customers
WHERE firstname = 'JORGE'
AND lastname = 'PEREZ');

b. SELECT referred FROM customers

WHERE (customer#, referred) = (SELECT customer#
FROM customers WHERE firstname = 'JORGE'
AND lastname = 'PEREZ');

c. SELECT referred FROM customers

WHERE (customer#, referred) IN (SELECT customer#
FROM customers WHERE firstname = 'JORGE'
AND lastname = 'PEREZ');

d. SELECT customer# FROM customers

WHERE customer# = (SELECT customer#
FROM customers WHERE firstname = 'JORGE'
AND lastname = 'PEREZ');