In the letter series r _ p r _ p _ q _ r _ p, which one set of letters, when inserted sequentially into the blanks, will correctly complete the pattern?

Introduction / Context:
This question again deals with a missing letter series, but this time only three letters r, p, and q are involved. The task is to determine which sequence of letters completes the pattern when placed into the blanks in order. Such problems help evaluate how effectively you can detect underlying repetition and structure, even when letters repeat in a seemingly complex way.

Given Data / Assumptions:

• The series is: r _ p r _ p _ q _ r _ p.
• There are five blanks; each option provides five letters that must be inserted sequentially.
• After filling, the final series should have a clear and consistent pattern, ideally in the form of a repeated block.

Concept / Approach:
Since the letters r, q, and p appear, a natural idea is that the series may be built from a small repeating unit such as rqp or rpq. To uncover this, we replace the blanks using each option and then examine the completed string. The correct option will give a simple repeated cycle that continues without disruption. This type of series is usually designed so that the completed pattern is obvious and compact once discovered.

Step-by-Step Solution:
Step 1: Identify blank positions at second, fifth, seventh, ninth, and eleventh places. Step 2: Try option B which supplies the letters q q r p q in order. Step 3: Insert them into the blanks to get: r q p r q p r q p r q p. Step 4: Group this series as r q p repeated four times: rqp rqp rqp rqp. Step 5: Observe that each block r q p is identical and follows immediately after the previous block, creating a neat cyclic pattern. Step 6: This shows that option B creates a perfectly regular repeating sequence, which is the hallmark of a correct completion.

Verification / Alternative check:
To verify, check that no letter appears in a position that breaks the r q p rotation. Starting at the first letter r, the sequence always progresses to q then to p, and then repeats from r again. There are no double q or double p blocks in places where the pattern would expect another letter. This uniformity confirms that option B fits the intended design of the question. A quick comparison with other options confirms that only option B leads to this clean repetition.

Why Other Options Are Wrong:
Option A (qrppq) leads to segments where double p appears and the rotation r q p is broken, so the series cannot be rearranged into identical blocks. Option C (qrprp) generates inconsistent transitions that do not match a single simple cycle. Option D (qrppr) produces an uneven distribution with extra p letters which again conflicts with any regular pattern. These irregularities show that these options do not create a consistent repeating sequence across all positions.

Common Pitfalls:
A common mistake is to choose an option that seems to make the first half of the series look reasonable without inspecting the entire completed sequence. Another pitfall is to focus on immediate neighbours but ignore longer cycles that extend over three or more positions. In letter series questions, it is very important to search for a small repeating block and verify that this block can be applied throughout the series without contradictions.

Final Answer:
The correct set of letters is option B, qqrpq.