In the letter series TU, DE, NO, which of the following pairs of letters should come next to continue the same alphabet pattern?

Introduction / Context:
This question provides a series of letter pairs: TU, DE, NO, ?. The task is to discover the underlying rule governing how these pairs are formed and then apply the same rule to determine the next pair. At first glance, the pairs appear unrelated, but careful analysis of letter positions in the alphabet reveals a consistent pattern involving forward and backward jumps.

Given Data / Assumptions:

• Given pairs: TU, DE, NO, ?.• Each term consists of two consecutive letters in natural order (for example, T and U).• The key change happens between the starting letters T, D and N.• The alphabet positions A=1, B=2, ..., Z=26 are used.

Concept / Approach:
We treat each pair as a unit specified by its first letter, since the second letter is always just one step ahead. Hence, we mainly study the sequence of first letters: T, D, N and then the unknown. By converting these letters to numbers and analysing the differences between them, we can discover a repeating pattern of jumps. Applying that pattern leads us to the next first letter and therefore the next pair.

Step-by-Step Solution:
Positions of first letters: T=20, D=4, N=14.From T to D, we can view the change as −16 or equivalently +10 (since 20 + 10 = 30, and 30 − 26 = 4).From D to N, the change is +10 (4 → 14).Thus the effective movement in the cyclic alphabet is +10 each time.Apply +10 to N (14): 14 + 10 = 24, which corresponds to X.Since each pair is made of consecutive letters, the second letter after X must be Y.Therefore the next pair is XY.

Verification / Alternative check:
We can verify this by rotating forward: starting from D (4), adding 10 gives N (14); from N (14), adding 10 gives 24, which is X. Checking with TU, we see that moving 10 positions forward from D gives N, and similarly from N gives X. No other pair among the options maintains this cyclic +10 jump in the starting letters while preserving the consecutive-letter structure inside each pair.

Why Other Options Are Wrong:
PQ begins at P (16) and would require a different jump from the existing pattern. FG and VW also fail to maintain the +10 rotation from N. Although these pairs are visually reasonable, they do not fit the exact numeric rule observed in the series. Hence, they do not qualify as the correct continuation.

Common Pitfalls:
One common mistake is to look only at the visible alphabetical order within each pair and ignore the relation between successive pairs. Another is to overlook the cyclic nature of the alphabet and treat negative jumps as unrelated. By explicitly converting letters to numerical positions and considering modular arithmetic on 26 letters, candidates can avoid such errors.

Final Answer:
XY