Using the university database from previous labs: (a) Run EXPLAIN on a JOIN query between STUDENT and ENROLMENT. Note the execution plan. (b) Add an index on STUDENT(Level) and ENROLMENT(CourseCode). Run EXPLAIN again and compare. (c) Write the SAME query in two different ways (using JOIN vs. subquery) and compare their EXPLAIN outputs. Which is faster? (d) Identify which column would benefit most from an index based on typical query patterns.