given this database:

Department (dcode, dname, chair) Course (dcode, cno, title, units) Prereq (dcode, cno, pcode, pno) Class (class, dcode, cno, instr) Faculty (ssn, name, dcode, rank) Student (ssn, name, major, status) Enrollment (class, ssn) Transcript (ssn, dcode, cno, grade)

I cant seem to resolve the diffences between these 3 questions:

9. Find classes (class, dcode, cno) in which at least two students are enrolled 10. Find classes (class, dcode, cno) in which at most two students are enrolled 11. Find classes (class, dcode, cno) in which exactly two students are enrolled