Choose the 4-letter block that continues the visible chunk pattern so each segment keeps the n/m counts and order: — n m m n — m m n n — m n n m —

Introduction / Context:
This is a block-based letter series built from n and m only. Each visible chunk shows a pattern of two letters and their counts (e.g., n m m n). The aim is to select the next 4-letter block that keeps the evolving order without breaking the count symmetry.

Given Data / Assumptions:

• Template of 4-letter chunks: nmmn, mmnn, mnnm, …
• Exactly four letters are to be inserted as the next block.
• Valid blocks must be permutations with two n’s and two m’s, preserving the progression by rotation.

Concept / Approach:
Observe that the chunks cycle by shifting the leading letter toward the back while preserving the 2n/2m composition: nmmn → mmnn → mnnm → (back to) nmmn. Hence the appropriate next block is again nmmn.

Step-by-Step Solution:

Verification / Alternative check:
Listing the cycle explicitly: nmmn → mmnn → mnnm → nmmn … confirms the 4-term loop.

Why Other Options Are Wrong:

• n n m m: Breaks the observed internal order within the chunk.
• n m n m: Alternating sequence, not consistent with the given blocks.
• m n n m: Represents the third chunk, not the next after it.
• None of these: Invalid because nmmn appears among the options.

Common Pitfalls:
Mistaking any 2n/2m permutation as valid; the sequence also encodes order/rotation, not just counts.

Final Answer:
n m m n