In Choose odd Letter Group type questions, usually five groups of letters are given. Four of them are similar to each other in some manner while one is different and this is to be chosen by the candidate as the answer.
ABCD , EGIK , ACDF , CFIL
The letters in (a) follow the sequence +1;
those in (b) follow the sequence +2 and those in (d) follow the sequence +3,
while the letter in (c) do not follow any such particular sequence.