Question: Find the last name of the student who has a cat that is age 3.
SQL: SELECT T1.lname FROM student AS T1 JOIN has_pet AS T2 ON T1.stuid  =  T2.stuid JOIN pets AS T3 ON T3.petid  =  T2.petid WHERE T3.pet_age  =  3 AND T3.pettype  =  'cat'