Select the letter-cluster that can replace the question mark (?) in the following series.
EFY, FID, GLI, HON, IRS, ?

The given alphabet series EFY, FID, GLI, HON, IRS,?

We know that alphabet position A=1, B=2, C=3, D=4 ........ Z=26 

then E= 5 , F=6, Y=25,  I=9, D= 4, G=7, L=12, H=8, O=15, N=14, R=18, S= 19 

then  the series  represent in the form alphabet position 

5 6 25, 6 9 4, 7 12 9, 8 15 14, 9 18 19, ?

then the series pattern going in the form first is increasing 1 position to the next second is increasing in 3 positions to the next and third is increasing in 5 positions to next

, therefore ? =  10 21 24 

? =  J U X (10  21 24) Ans