Question 4 Not yet answered To add a foreign key constraint to table "registration" that is references to table "students". which of the following statements is correct? Marked out of 1.00 P Flag question a. Alter table registration add(constraint st_cons foreign key(student_id) references students(id)); O b. Alter table students add(constraint st_cons foreign key(student_id) references students(id)); c. Alter table registration add(constraint st_cons references students(id)); O d. Alter table registration add(constraint st_cons foreign key (id) references students(id)); Question 5 To change NULL values of the column "Mark" in the table "Exam_results" to 0, write the query: Not yet answered Marked out of 1.00 P Flag question a. update Exam_results set Mark = NULL where Mark =0; O b. alter table Exam_results set Mark = 0 O c. update Exam_results set Mark = 0 where Mark is NULL: O d. A or C. Question 6 Which statement will erase all records in Registration table? Not yet answered Marked out of 1.00 a. Drop table Registration O b. Delete from Registration O c. Delete * from Registration O d. B and C. P Flag