Which one set of letters, when sequentially placed in the blanks, will complete the repeating letter series H__JH__IJHHI__HH__JH?

Introduction / Context:
This question gives a partially hidden letter series H__JH__IJHHI__HH__JH and asks you to choose a set of four letters that, when placed in the blanks in order, completes a regular pattern. This is a typical letter series completion problem where a short block of letters repeats several times. Recognising the repeating unit is the quickest way to reach the correct answer.

Given Data / Assumptions:

• Original pattern with four blanks: H__JH__IJHHI__HH__JH.
• Each answer option provides four letters to be inserted from left to right into the four blank positions.
• We are looking for a simple, regular repetition of a short group of letters.
• The main letters present repeatedly are H, I, and J.

Concept / Approach:
A good approach is to suspect that the sequence is built from a small repeating block, for example HIJH or HJIH. We can test each option by filling the blanks and then checking whether the resulting full series can be divided into equal sized repeating groups. The correct set of letters should produce a pattern that is both simple and uniform throughout the entire string.

Step-by-Step Solution:
Step 1: Represent each pair of underscores as a single blank and rewrite the skeleton as H x1 J H x2 I J H H I x3 H H x4 J H. Step 2: Try option A, which gives the letters I, H, J, I for x1, x2, x3, x4 respectively. Step 3: Substitute them: the sequence becomes H I J H H I J H H I J H H I J H. Step 4: Now group the final sequence into blocks of four letters: HIJH | HIJH | HIJH | HIJH. Step 5: We can see that the block HIJH repeats exactly four times without any break, so the pattern is extremely regular.

Verification / Alternative check:
To be certain, quickly test other options. For example, using option B (H, I, H, I) gives a string which, when grouped, does not produce four identical blocks. Irregularities appear in the positions of I and J, which shows that the underlying pattern is broken. Option C and option D similarly fail to create a fully consistent repetition of any simple four letter sequence. Only option A produces a full series that is a clean repetition of HIJH.

Why Other Options Are Wrong:
Option B H I H I leads to a mixture of segments where the position of J changes unpredictably, so you cannot find a single block that repeats. Option C I H I J and option D H J H J also fail to generate four identical consecutive blocks and create asymmetrical patterns. Since the question expects one neat repetitive series, any option that does not give a perfect repetition of a four letter block must be rejected.

Common Pitfalls:
A common mistake is to focus only on filling the first blank and then guessing the rest without checking the entire completed string. Another pitfall is to look for a complicated rule instead of checking the simplest possibility: a short repeating block. Writing the full sequence for a promising option and grouping it into equal parts is the most reliable way to avoid confusion.

Final Answer:
The correct set of letters is I H J I, which makes the series a repetition of HIJH four times.