Which of the given letter-clusters will replace the question mark (?) in the following series?

BZTR, DBVT, FDXV, ?, JHBZ

HFZX

Explanation:

BZTR, DBVT, FDXV, ?, JHBZ

The logic followed here is :

B → (+2) → D → (+2) → F → (+2) → H → (+2) → J

Z → (+2) → B → (+2) → D → (+2) → F → (+2) → H

T → (+2) → V → (+2) → X → (+2) → Z → (+2) → B

R → (+2) → T → (+2) → V → (+2) → X → (+2) → Z

So, the letter-cluster that replaces the (?) to complete the series is "HFZX"