Two-letter terms: both letters +2 (CE, EG, GI ...)

The same question, asked 3 times: 21 Sep 2025 S1*, 23 Sep 2025 S2*, 23 Sep 2025 S3. Every wording below, oldest first.

Try each one first, then open its answer.

Question 1
21 Sep 2025 S1
21 $What comes next? CE, EG, GI, ?$
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Question 2
23 Sep 2025 S2
17 $What comes next? AF, CH, EJ, ?$
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Question 3
23 Sep 2025 S3
13 $What comes next? CG, EI, GK, ?$
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