useing schema answer:

1)

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;

2)

The query that displays computer networks students :

a.

select full_name from students where Major_name = 'computer networks' ;

b.

select full_name,major_id from students natural join majors where Major_name = 'computer networks' ;

c.

select full_name from students join majors using(students.major_id = majors.major_id) where Major_name = 'computer networks' ;

d.

select full_name from students where Major_id = 124;

3)

a.

select course_level , count(course_id) from courses having course_level 1 group by course_level ;

b.

select course_level , count(*) from courses group by course_level having course_level

c.

select count(course_id) from courses group by course_level where course_level >1;

d.

None of the above.

Exam_results Majors Major_id: number(3) Major_name: varchar2(50) Department_name: varchar2(50) Faculty:varchar2(50) Student_id: number(10) Course_id: number(10) Exam_name: varchar2(50) Max_mark: number(5,2) Mark:number(5,2) courses Students Course_id: number(10) Course_name:varchar21 100) Credit_hours:number(2) Course_level:number(2) Teachers Teacher_id: number(5) Teacher_name:varchar2 (50) Department_name:varc har2(10) ID: Number(10) Full_name: Varchar2(50) Address: varchar2(50) Bd:date Gender: char(1) Major_id: number(3) Registration_date: date Semester Semester_id: number(5) Start_date: date End_date: date Description:varchar2(50) Registration Student_id: number(10) Course_id: number(10) Semester_id: number(5) Teacher_id: number(5) Result_number: number(5,2) Result_letter: char(1)