21- To find the name of the student that has the maximum mark in the exam named first exam , we can use:

a. select full_name from students where id in(select student_id from exam_results where mark=(select max(mark) from exam_results where exam_name='first exam'));

b. select full_name from students where mark=(select max(mark) from exam_results where exam_name=first_exam);

c. select full_name from students s join exam_results er on(s.id=er.student_id) where er.mark in(select max(mark) from exam_results where exam_name=first exam);

d. Both A and C.

22- A query to deletes all semesters with a description 'summer semester'.

a. DELETE FROM semester;

b. DELETE FROM semester WHERE semester_id =(SELECT semester_id from semester where description like '%summer');

c. DELETE FROM semester WHERE semester_id =(SELECT semester_id from semester where description like 'summer%');

d. truncate table semester;

23- The query:

select max(course_level) from courses join registration using(course_id);

displays:

a. Makes error.

b. The maximum course level in table courses.

c. The maximum course level for the courses registered in table registration.

d. The maximum course_id in table registration.

24- select months_between(start_date,end_date) from Semester; will show a report of the length of all semesters;

a. True

b. Flase