In the following question, which one set of letters, when sequentially placed at the gaps in the given letter series, will complete it? b_d_ed_b_c_e

Introduction / Context:
This is a letter-series completion problem. A sequence of letters is given with several blanks, and you are asked to choose one set of letters that, when inserted in order, makes the entire series follow a clear pattern. The difficulty here lies in noticing that the pattern involves letters going forward and backward in the alphabet in a symmetric way.

Given Data / Assumptions:
- Incomplete series: b_d_ed_b_c_e
- There are five blanks in this series.
- Each option provides a 5-letter string to be inserted, in order, into the blanks.
- We must choose the set that creates a meaningful and consistent pattern through the whole series.

Concept / Approach:
The usual approach in such problems is:
- Step 1: Write down the complete series after inserting the letters from each option.
- Step 2: Look for simple alphabetical progressions or symmetrical patterns such as increasing then decreasing sequences.
- Step 3: Select the option that produces a clean, repeating pattern without breaks or contradictions.

Step-by-Step Solution:
Step 1: Insert option (b) “cecbd” into the blanks. The series becomes: b c d e e d c b c d e. Step 2: Now observe the pattern. From the first letter: b, c, d, e form an ascending sequence in the alphabet. Step 3: Next, from position 5 to 8: e, d, c, b form a descending sequence, which is the reverse of b, c, d, e. Step 4: Finally, from position 8 to 11: b, c, d, e again form the same ascending sequence. Step 5: Thus, the complete pattern is: ascending (b c d e), then descending (e d c b), then ascending again (b c d e). Step 6: Check that no letter breaks this symmetry. The pattern is smooth and fully consistent.

Verification / Alternative check:
Test the other options quickly:
- Option (a) produces “bcdeedbbcce”, which does not show a clean symmetrical pattern.
- Option (c) and option (d) similarly create irregular sequences without a neat ascending–descending structure.
Option (b) is the only one that gives the aesthetically clear pattern of b c d e, then e d c b, then b c d e.

Why Other Options Are Wrong:
- “cedbc”: The resulting series contains awkward repetitions and fails to form a simple, recognisable alphabet pattern.
- “ceabc”: Produces a mixed sequence with no consistent ascending or descending order.
- “cecdb”: Breaks the symmetry and injects letters at places where the pattern would otherwise rise or fall smoothly.

Common Pitfalls:
Students often try to match only local patterns (for example, looking at just three or four letters) instead of scanning the entire string. Another mistake is to focus only on frequency of letters rather than the order. For letter-series questions, think in terms of direction (forward or backward in the alphabet) and repetition of full blocks rather than isolated pairs.

Final Answer:
The set of letters that correctly completes the series is “cecbd”.