Four-letter clusters: letters move +4, -2, +4, -2

The same question, asked 2 times: 19 Sep 2024 S3*, 23 Sep 2024 S1. Every wording below, oldest first.

Try each one first, then open its answer.

Question 1
19 Sep 2024 S3
21 $Which of the following terms will replace the question mark (?) in the given series? HDLB, LBPZ, PZTX, ? , XVBT$
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Question 2
23 Sep 2024 S1
2 $Which of the following terms will replace the question mark (?) in the given series? JHOQ, NFSO, ? , VBAK, ZZEI$
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