1. (SELECT S.sname FROM Students S, Faculty F, Enrolled E, Class C
   WHERE F.fid=C.fid AND E.cname = C.cname AND E.snum = S.snum AND F.fname = 'I. Teach');
   
   
2. SELECT MAX(age)
   FROM Student, Enrolled, Class, Faculty
   WHERE (major = 'history') OR (Faculty.fid = Class.fid AND Class.cname = Enrolled.cname
   							   AND Enrolled.snum = Student.snum);
   							   
3. SELECT name
   FROM Class
   WHERE room = 'R128'
   UNION
   SELECT name
   FROM Class, Enrolled
   WHERE (SELECT COUNT(snum) FROM Enrolled) > 4;
   
 4. SELECT name
 	FROM Class C1, Class C2, Student S, Enrolled E
 	WHERE S.snum = E.enum AND E.cname = C1.cname AND E.cname = C2.cname 
 		  AND C1.cname !=C2.cname AND C1.time = C2.time;
 	
 	
 5. SELECT fname 
 	FROM Faculty F, Class C1, Class C2, Class C3
 	WHERE F.fid = (SELECT fid FROM C1 MINUS C2 MINUS (SELECT room from C1);
 	
 //wrong6. SELECT fname 
 	FROM Faculty 
 	WHERE fid = ((SELECT fid FROM ((SELECT COUNT(fid) FROM Class) < 5));
 	
 7. PRINT level, AVG(age)
 	FROM Student
 	WHERE level = 'FR';
 	PRINT level, AVG(age)
 	FROM Student
 	WHERE level = 'SO';
 	PRINT level, AVG(age)
 	FROM Student
 	WHERE level = 'JU';
 	PRINT level, AVG(age)
 	FROM Student
 	WHERE level = 'SR';
 	
 	
 8. PRINT level, AVG(age)
 	FROM Student
 	WHERE level = 'FR';
 	PRINT level, AVG(age)
 	FROM Student
 	WHERE level = 'SO';
 	PRINT level, AVG(age)
 	FROM Student
 	WHERE level = 'SR';
 	
9. SELECT sname 
   FROM Student
   WHERE snum = (SELECT MAX(SELECT COUNT(snum) FROM Enrolled) FROM Enrolled)
   

10. SELECT sname
	FROM Student
	WHERE snum NOT IN(SELECT snum FROM Enrolled);
	
	
11.