Select the letter-cluster from among the given options that can replace the question mark (?) in the following series.

LAS, IYR, FWQ, CUP, ?

ZSO

Pattern followed is :

LAS, IYR, FWQ, CUP, ?

(1ST letter of each group)    L - 3 = I , I -3 = F , F - 3 = C , C - 3 = Z

(2nd letter of each group)     A - 2 = Y , Y - 2 = W , W - 2 = U , U - 2 = S 

(3rd letter of each group)    S - 1 = R , R - 1 = Q , Q - 1 = P , P-1 = O 

ZSO is correct answer .