Write SQL queries based on the following database Schema:

classroom(building, room_number, capacity)

department(dept_name, building, budget)

course(course_id, title, dept_name, credits)

instructor(ID, name, dept_name, salary)

section(course_id, sec_id, semester, year, building, room_number, time_slot_id)

teaches(ID, course_id, sec_id, semester, year)

student(ID, name, dept_name, tot_cred)

takes(ID, course_id, sec_id, semester, year, grade)

advisor(s_ID, i_ID)

time_slot(time_slot_id, day, start_time, end_time)

prereq(course_id, prereq_id)

(Join tables using WHERE condition or NATURAL JOIN)

4. Find the IDs of all students who had an instructor named Sullivan; make sure there are no duplicates in the result. (join multiple tables)

5. Find the names of all students who have taken at least one Comp. Sci. course; make sure there are no duplicates in the result. (join multiple tables)