Complete the letter series by filling the five blanks so that the same 4-letter pattern repeats throughout. Series: _ b b _ c _ b g _ b _ g

Introduction / Context:
Letter-series questions often hide a short repeating block. Your goal is to recover the missing characters so the whole sequence follows one uniform cycle. Recognizing the repeating unit is faster and more reliable than trying to place letters locally.

Given Data / Assumptions:

• Series with five blanks: _ b b _ c _ b g _ b _ g
• Options provide the five letters to insert, in order, from left to right.
• Exactly one option should produce a clean, repeating pattern across the entire string.

Concept / Approach:
For series-completion problems with multiple blanks, test whether the completed line forms equal-sized repeating chunks. A consistent 4-letter cycle is common in such formats. After placing a candidate option, we check if every consecutive 4-character block matches the same motif.

Step-by-Step Solution:

Verification / Alternative check:
Verify by sliding a 4-position window across the whole string. Each window reads "c b b g". No deviation appears, confirming the cycle length and correctness.

Why Other Options Are Wrong:

• cbgbc: Produces mixed blocks that do not repeat uniformly.
• cgbcc: Breaks the 4-letter cadence; partial matches appear but not end-to-end.
• gbcbb: Creates uneven transitions and mismatched blocks.

Common Pitfalls:
Focusing on local adjacency can be misleading. Always check the global cycle. Do not force alternating patterns without verifying full-length periodicity. Be careful to insert letters strictly in the left-to-right order of the blanks.

Final Answer:
cgbcb