In the letter series W _ Y Z _ X _ Z W _ Y _, which one set of letters, when placed sequentially in the blanks, will correctly complete the pattern?

Introduction / Context:
This question revolves around a letter series constructed from W, X, Y, and Z with several missing positions. To solve it, we need to identify an option whose letters complete the series so that it follows a simple and recognisable pattern. Many such questions use direct repetitions of a short sequence, and the ability to detect that repeated block is the main skill being tested.

Given Data / Assumptions:

• Incomplete series: W _ Y Z _ X _ Z W _ Y _.
• There are five blanks to be filled sequentially.
• Each option provides five letters to insert into these blanks in order.
• The final series should display an orderly repetition of the same four letter block.

Concept / Approach:
The presence of W, X, Y, and Z strongly suggests the block W X Y Z or some cyclic rotation of these letters. A reasonable hypothesis is that the full sequence may be multiple repetitions of W X Y Z. To test this, we fill the blanks with each option and inspect the result. The correct option will recreate exactly the block W X Y Z repeated several times, without any letter being out of place.

Step-by-Step Solution:
Step 1: Note that the blanks are at positions 2, 5, 7, 10, and 12. Step 2: Try option D, which provides the letters X W Y X Z. Step 3: Insert them into the series to obtain: W X Y Z W X Y Z W X Y Z. Step 4: Group the sequence as WXYZ WXYZ WXYZ. Step 5: Each group of four letters is exactly W X Y Z, which is consistent and highly structured. Step 6: The completed sequence is therefore composed of three identical WXYZ blocks, confirming a very clean pattern.

Verification / Alternative check:
To verify, check each group of four letters: positions 1 to 4, 5 to 8, and 9 to 12 all read W X Y Z with no deviation. This repetition matches the natural order of the four letters and is unlikely to be accidental. Testing other options results in misordered segments or extra repeated letters that break any simple four letter cycle. Hence only option D satisfies the requirement of a neat repeated W X Y Z pattern across the entire series.

Why Other Options Are Wrong:
Option A (ZWZXX) leads to clusters of X at the end and does not generate repeated W X Y Z blocks. Option B (YWYYZ) creates uneven groups, with extra Y letters, and cannot be partitioned into identical four letter units. Option C (XWYYZ) likewise produces irregular segments in which the order of W, X, Y, and Z is not consistent. None of these options manage to align the entire series into three complete W X Y Z units, which is why they are incorrect.

Common Pitfalls:
Learners may be tempted to stop after partially matching the visible letters or after making the first four or five letters look neat, without inspecting the entire completed series. Another common mistake is to ignore the idea of repeated short blocks and instead look only for adjacency rules, such as W followed by X. In many exam series questions, the shortest repeating block concept is central, so it is important to always test for this possibility when letters cycle through a small ordered set.

Final Answer:
The correct set of letters is option D, XWYXZ, producing the repeated series WXYZ WXYZ WXYZ.