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

ABCD, HGLO, OLUZ, VQDK, ?

Directions : Study the following alphanumeric series carefully and answer the questions given below:

12AIFR                  42 WBOL                             63EOCN                15TVMR               75GYTR

How many meaningful words can be formed from the letters of the words which are attached with the numbers in which At least one digit is even digit in the given alphanumeric series?

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

VTHJ ? TRJL SOKM  RPLN 

Which letter-cluster will replace the question mark (?) to complete the given series?
 ABCD, BDFD, CFID, ?, EJOD

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

LMR, PUA, TCJ, XKS, ?

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

RLV, PNS, NPP, ?, JTJ

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

QRM, PWD, OBU, NGL, ?

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

MDSA, KERC, ?, GGPG, EHOI