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

ABCD, FVJV, KPQN, PJXF, ?

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

ACFD, CFHG, ?, GLLM, IONP

Which one set of letters when sequentially placed at the gaps in the given letter series shall complete it?
 _bc_ca_aba_c_ca

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

AYD, BVF, DRH, ?, KGL

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

ZUPK, YTOJ, ?, WRMH, VQLG

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

REV, UXD, XQL, AJT, ?

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

TMT, ZOB, FQJ, LSR, ?

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

LE, OJ, UO, DT,?