Select the related word/letters/number from the given alternatives.CD : PQ :: GH : ?

Let's look at the alphabetical positions:C = 3, D = 4P = 16, Q = 17The difference between the first letters:$16-3=13$ The difference between the second letters:$17-4=13$ Applying the same $+13$ logic to GH:G = 7, H = 8First letter: $7+13=20\to \text{T}$ Second letter: $8+13=21\to \text{U}$ Therefore, GH relates to TU.