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?
 WFBI, UCWB, SZRU, ?

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

ABCD, HGLO, OLUZ, VQDK, ?

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?

MDSA, KERC, ?, GGPG, EHOI

Which letter-cluster will replace the question mark (?) to complete the given series?
 CZNM, FXOL, IVPK, ?, ORRI

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?

QRM, PWD, OBU, NGL, ?