Letter clusters: the step itself changes from term to term (-1, -2, -3 ...)

This type of question, asked 4 times: 17 Jul 2023 S4, 25 Jul 2023 S4, 9 Sep 2024 S3, 13 Sep 2024 S1. All 4 questions below, oldest first.

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Question 1
17 Jul 2023 S4
25 $Which of the following terms will replace the question mark (?) in the given series? SHP, RIO, PKN, MNM, ?$
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Question 2
25 Jul 2023 S4
22 $Which of the following terms will replace the question mark (?) in the given series? AXY, EZW, ICU, OHS, ?$
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Question 3
9 Sep 2024 S3
2 $Which of the following terms will replace the question mark (?) in the given series? MFT, NIS, PLQ, SON, WRJ, ?$
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Question 4
13 Sep 2024 S1
24 $Which of the following terms will replace the question mark (?) in the given series? KES, MIQ, PMN, TQJ, YUE, ?$
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Question 1