Segment 4 ("writing in long hand is becoming a vanishing art") is a complete opening statement, so it's A. Segment 3 ("thanks to mobile testing and computer literacy") gives the reason, so it follows as B. Segment 2 ("education groups asking for handwriting classes") is the consequence, so it's C. Segment 1 ("to see that students do not forget to write") explains the purpose, closing as D.
Full sentence: "Writing in long hand is becoming a vanishing art, thanks to mobile testing and computer literacy, the education groups are now asking for hand writing classes, to see that students do not altogether forget to write especially during exam time."
Order: 4,3,2,1 = A,B,C,D. So segment 3 is at position B.