Study the following series.
4 S I H N 8 A Y E 2 B P + Z 7 M T D 3 G
Find what should come in place of the question mark(?)
N8 , Y2 , ? , ZD
There is a gap of 2 between the first characters of each of the given pair. The second character of each pair is increasingly moving one position to the right of the first character.