Using the university schema, fill in the blank to complete the SQL query that finds, for each department, the maximum salary of instructors in that department.
a) SELECT department, MAX(salary) FROM instructors GROUP BY department;
b) SELECT department, MAX(salary) FROM university GROUP BY instructors;
c) SELECT department, MAX(salary) FROM instructors WHERE department = university;
d) SELECT department, MAX(salary) FROM university WHERE instructor = MAX(salary) ;