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

Which letter-cluster will replace the question mark (?) to complete the given series?

LE, OJ, UO, DT,?

In the following question, which one set of letters when sequentially placed at the gaps in the given letter series shall complete it? 

_cca_a_ca_ac_ab

In each of the following letters series, some of the letters are missing which are given in that order as one of the alternatives below it. Choose the correct alternative.
aa _ _ aba _ bca _ aab _ a _

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

Select the option that represents the letters that, when sequentially placed from left to right in the blanks below, will complete the letter series.
 _ M o N _ _ _ o M _ _ o _ _o M _ N o J o

Which of the following letter-clusters will replace the question mark (?) and complete the following letter-cluster series?
 DW, FU, GT, IR, JQ, ?

Which letter cluster will replace the question mark (?) to complete the given series?
 WFBI, UCWB, SZRU, ?