Direction: In a school the periodical examination are held every second month. In a session during April 2001 - March 2002, a student of Class IX appeared for each of the periodical exams. The aggregate marks obtained by him in each perodical exam are represented in the line-graph given below. Marks Obtained by student in Six Periodical Held in Every Two Months During the Year in the Session 2001 - 2002.

1.  

In which periodical exams did the student obtain the highest percentage increase in marks over the previous periodical exams ?