What is the code of the course which the student whose last name is Smithson took?
SELECT T1.crs_code FROM CLASS AS T1 JOIN enroll AS T2 ON T1.class_code  =  T2.class_code JOIN student AS T3 ON T3.stu_num  =  T2.stu_num WHERE T3.stu_lname  =  'Smithson'
Smithson'un soyadı olan öğrencinin aldığı kursun kodu nedir?