Which ordered set of letters, placed into the blanks in sequence, completes the series? C D_E_D D_C D_E

Introduction / Context:
This is a “fill the gaps with a chosen ordered set” type of letter-series question. Unlike inserting independent letters, here we must take one option (four letters, given with spaces for readability) and place its letters into the blanks in the exact left-to-right order to make the entire sequence coherent.

Given Data / Assumptions:

• Base pattern with underscores: C D _ E _ D D _ C D _ E
• One ordered 4-letter sequence must be inserted sequentially at the four blanks.

Concept / Approach:
Look for recurring micro-motifs like “C D E D” or “D C D E” that can tile the string with minimal conflict. The visible fragments “C D” at the start and “D _ E” at the end suggest a symmetric completion using D and E around C to form repeating triplets/quartets.

Step-by-Step Solution:
1) Test option “D C E D”. Place D at the first blank: C D D E …2) Place C at the second blank to get C D D E C D, which exhibits a smooth C–D–E movement.3) For the third blank (in “D _ C”), insert E so it becomes D E C, keeping the earlier D–E pattern intact.4) For the final blank (in “D _ E”), insert D so the tail becomes D D E, aligning with the motif near the start.5) The full string reads consistently with repeating C/D/E ordering when the placements are applied as D, C, E, D.

Verification / Alternative check:
Quickly re-scan for contradictions such as doubled letters that violate adjacency logic or broken small runs. The completed sequence maintains a coherent interleaving of C, D, and E.

Why Other Options Are Wrong:

• C D C D: Produces clumps that block the needed E insertions at two locations.
• D C C C: Overloads Cs, breaking the visible D–E alternations.
• D D D C: Forces long D runs and a single C tail, inconsistent with central fragments.

Common Pitfalls:
Many test takers fit the first two blanks but fail to check the last two positions. Always place all four letters and then re-check the entire sequence.

Final Answer:
D C E D