In the letter series efg__eff_ghhe_eff_gggh_h, which one set of letters, when sequentially placed in the blanks, will correctly complete the pattern?

Introduction / Context:
In this question you are given a letter series with several blanks: efg__eff_ghhe_eff_gggh_h. You must choose a six letter sequence that, when placed in the blanks from left to right, produces a smooth, regular pattern. The letters used are e, f, g, and h, and the completed string reveals a very neat structure of repeated groups with increasing counts of each letter.

Given Data / Assumptions:

• Skeleton pattern: efg _ _ eff _ ghhe _ eff _ gggh _ h.
• There are six blanks to be filled in order.
• Options: eghhfe, ghhhh, hegefh, hgefhe, egeffh.
• We expect a clear, systematic repetition of e, f, g, h once the blanks are filled.

Concept / Approach:
A good way to see the pattern is to try a promising option and examine whether the resulting string can be broken into meaningful blocks. For alphabet series built from a small set of letters, exam setters often create sequences where each group increases the number of times each letter appears. Here, using the correct option yields distinct blocks like efgh, eeff, gghh, eeefff, and ggghhh.

Step-by-Step Solution:
Step 1: Label the blanks x1 to x6 and rewrite the sequence as e f g x1 x2 e f f x3 g h h e x4 e f f x5 g g g h x6 h. Step 2: Try option C, hegefh, which assigns x1 h, x2 e, x3 g, x4 e, x5 f, x6 h. Step 3: Substitute these values. The final sequence becomes: e f g h e e f f g g h h e e e f f f g g g h h h. Step 4: Group this sequence into meaningful blocks: efgh | eeff | gghh | eeefff | ggghhh. Step 5: Observe the structure. The first block efgh has each letter once. The second block eeff has two e and two f. The third block gghh has two g and two h. The fourth block eeefff has three e and three f. The fifth block ggghhh has three g and three h.

Verification / Alternative check:
The completed pattern shows a clear and elegant design: counts of letters increase from one to two to three, and e and f are grouped together, while g and h form their own group. No other option leads to such a clean sequence of blocks. If we try option A or D, the mixture of letters does not split into balanced groups like eeff or gghh, and the counts of each letter within a block become irregular. Option B and E also fail to create structured growth from one to two to three occurrences.

Why Other Options Are Wrong:
Using eghhfe or hgefhe or egeffh in the blanks leads to sequences where at least one block mixes letters unevenly, for example three letters of one type with only one of another, or does not produce distinct stages like efgh, eeff, gghh, and so on. The set ghhhh has only five letters and cannot even supply a unique letter for each blank, making it impossible to complete the pattern correctly. Thus these options do not result in an orderly, increasing repetition of letters.

Common Pitfalls:
Many candidates look only at the first few letters and try to match small segments without inspecting the structure of the entire sequence. Others expect a simple fixed step pattern between individual letters, rather than grouping letters into larger blocks. The most reliable method is to fill the blanks with each candidate set, then attempt to group the resulting string into visually or numerically balanced blocks. The block based pattern is very obvious once the correct letters are in place.

Final Answer:
The set of letters that correctly completes the series is hegefh, producing the blocks efgh, eeff, gghh, eeefff, and ggghhh.