Question 21 What will be the output of the following query: Not yet answered Marked out of 1.00 select id,full_name to_char(null) from students union all select teacher_id, teacher name department_name from teachers: P Flag question O a. A combination of the results of the 2 queries, the common results will be shown once. O b. A combination of the results of the 2 queries, the common results will be shown twice c. Error: columns data types mismatch. d. Error: number of columns mismatch. Question 22 A query to display the second highest Mark in the exam_results table. Not yet answered Marked out of 1.00 Flag question a. SELECT MAX(mark) AS "2nd_mark" FROM exam_results: O b. SELECT MAX(MAX(mark)) AS "2nd_mark" FROM exam_results: OC. SELECT MAX(mark) AS "2nd_mark" FROM exam_results WHERE mark (SELECT MAX(mark) FROM exam_results)