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?
 ERKV, HYVK, ?, NMRO, QTCD

Which letter-cluster will replace the question mark (?) to complete the given series?
 ZFOE, PYUA, FRAW, VKES, ?

Which letter-cluster from the options will replace the question mark (?) to complete the given series?
 ASDF, BUGJ, CWJN, ?

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?

VTHJ ? TRJL SOKM  RPLN 

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

RLV, PNS, NPP, ?, JTJ

In the word ‘LAVISLY’, replace each vowel with the next letter in the alphabetical series and each consonant with the previous letter in the Alphabetical Series. How many letters occur more than once in this newly formed word?