The series is having 5,4,3,2,1 as difference in letters positions from left to right . That means Position of J is 10 , E's position is 5 . Hence difference between positions is 10-5=5, same way for T and P which leads to 20-16=4 . Using same logic you will get Positional difference between P and M as 3 , Z and Y as 1 . Hence the missing letters positional difference must be two . The best fit in the given options is CA and whose positional difference is 2 .