From a database that contains the tables EMPLOYEE(emp_num,name,profession), PRODUCT(prod_id,product_name,details), ASSIGNMENT(emp_num,prod_id,desig_id) and TITLE_DESIGNATION(desig_id,title) provide an SQL query that finds the prod_id of products that do not have managers assigned to work on them.

Select one:

a. select prod_id from ASSIGNMENT where prod_id not in

(select a.prod_id

from ASSIGNMENT a, TITLE_DESIGNATION t

where t.title = 'manager' and a.desig.id = t.desig_id);

b. select a.prod_id from ASSIGNMENT a, EMPLOYEE e where e.emp_num = a.emp_num and not (e.profession = 'manager');

c. select p.prod_id from PRODUCT p, ASSIGNMENT a where p.emp_num = a.emp_num

d. select prod_id from PRODUCT where not exists

(select emp_num

from EMPLOYEE

where profession = 'manager');