Hey,

In this question the second letter is the letter 4 positions ahead of the first letter in Alphabet.

That is,

A is the first letter of alphabet and E is the 5th letter. therefore ae,

like this, B is second and F is the sixth letter, BF

like the above pattern CG and DH are observed thus, the next letters in the series will be EI, FJ ... and so on.

I hope this helps.

All the best!