Letter series with blanks: 4-letter groups where every position moves by its own step

This type of question, asked 3 times: 24 Sep 2024 S1, 24 Sep 2024 S2, 24 Sep 2024 S3. All 3 questions below, oldest first.

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Question 1
24 Sep 2024 S1
15 $Select the combination of letters that when sequentially placed in the blanks of the given series will complete the series. _TUVTR_WU_UXVN_Y$
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Question 2
24 Sep 2024 S2
7 $Select the combination of letters that when sequentially placed in the blanks of the given series will complete the series. LM_O_NPMRO_KU_TI$
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Question 3
24 Sep 2024 S3
4 $Select the combination of letters that when sequentially placed in the blanks of the given series will complete the series. B_DE_GDGBK_IB_DK$
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Question 1