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

RMTS, WGAK, BAHC, GUOU, ?

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?

ZUPK, YTOJ, ?, WRMH, VQLG

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

TTDS, VMLP, XFTM, ZYBJ, ?

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?

AVTE CTRG ERPI GPNK   ?

Which letter cluster will replace the question mark (?) to complete the given series?
 ANGE, DSBB, GXWY, ?

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

CABQ, CEJC, CIRO, CMZA, ?