In the following letter series, some letters are missing and are shown as blanks. The missing letters occur in the same left to right order as in one of the options. Choose the option that correctly completes the series ba_ba_bac_acb_cbac.

Introduction / Context:

This letter series question hides a repeating pattern and uses blanks to break the visible repetition. The task is to fill the blanks with letters in such a way that the entire series becomes a smooth repetition of a smaller block of letters. Such problems test the ability to detect repeating units and to associate the order of missing letters in the main series with the order of letters in the answer options. This is a common type of question in verbal reasoning and logical ability examinations.

Given Data / Assumptions:

• The incomplete series is written as ba_ba_bac_acb_cbac.
• Blanks represent missing letters that must be placed in the order given by one of the options.
• Each option is a four letter string, and these four letters replace the blanks in sequence from left to right.
• The completed series should exhibit a clear and consistent pattern, ideally a simple repetition.

Concept / Approach:

The natural strategy is to consider that the series might be composed of a repeated block such as bac. We can attempt to fill the blanks with the letters from each option and then inspect the final string. The correct option should transform the messy looking series into something that showcases a neat repetition or easily describable order. Rather than relying on intuition alone, we systematically test each option by substitution and see whether a recognizable repeating group emerges.

Step-by-Step Solution:

Step 1: Represent the pattern with underscores as ba_ba_bac_acb_cbac, where there are four blanks. Step 2: Take option ccba and substitute its letters into the blanks in order: first c, second c, third b, fourth a. Step 3: After substitution, the string becomes bacbacbacbacbacbac, which is bac repeated six times. Step 4: Observe that bac is a three letter block, and the entire completed series consists solely of this block in perfect repetition. Step 5: This level of regularity strongly indicates that option ccba is the intended choice.

Verification / Alternative check:

To verify, we can also test the other options briefly. Substituting bbca, cbac, aacb, or bcca does not produce a simple uniform repetition. Their completed strings contain irregular segments and do not reduce to consistent repeated units. Only when we use ccba do we obtain bacbacbacbacbacbac with no deviations. That is a very strong confirmation, as exam questions of this type are designed around clear and elegant patterns like exact repetition of a small group.

Why Other Options Are Wrong:

Option bbca leads to a complex mixture that does not display any simple repeating unit. Option cbac also fails to generate a recognizably repeated three letter pattern across the entire string. Option aacb similarly produces a fragmented sequence instead of a neat repetition. Option bcca has no interpretation that yields a consistent repeated block. Because exam series questions aim for concise underlying structures, these irregular outcomes are not acceptable. Therefore, none of these options matches the elegant bac repetition that we get from ccba.

Common Pitfalls:

Students sometimes try to analyze the series purely from left to right without considering that a smaller repeating block may lie beneath the surface. Another common mistake is to stop after checking only the first few letters after substitution, rather than confirming that the entire completed sequence follows the same pattern. Some learners also rely on visual similarity instead of actually writing out the full string, which can hide inconsistencies. A careful and complete substitution check prevents these errors.

Final Answer:

The only option that converts the series into a clean repetition of the block bac is ccba, so that is the correct set of missing letters.