In the following question, which one set of letters when sequentially placed in the blanks will complete the series m_o_mn_p_no_ correctly?

Introduction / Context:
This is a letter completion problem where a partially given series m_o_mn_p_no_ must be completed by inserting one of the provided five letter sequences into the blanks. The completed word like structure should expose a clear pattern. Recognising repeated alphabetic blocks is central to solving this type of question.

Given Data / Assumptions:

• The incomplete pattern is m _ o _ m n _ p _ n o _.
• There are five blanks to be filled, from left to right, with the letters from exactly one of the options.
• Options are mmnno, ooppn, mnooo, and npomp.
• The final sequence should exhibit a systematic structure rather than random letters.

Concept / Approach:
An effective approach is to substitute each option into the blanks and then examine the completed sequence. We look for a recognisable pattern such as repeating groups of letters or a clear alphabetical progression. Since the visible letters already suggest something close to mnop repeating, checking for an mnop block is sensible.

Step-by-Step Solution:
Step 1: Identify where the blanks appear. The pattern is m _ o _ m n _ p _ n o _, so the blanks are at positions 2, 4, 7, 9, and 12. Step 2: Insert option mmnno into the blanks. The resultant sequence is mmommnnpnnoo, which looks irregular and does not suggest a simple repeating block. Step 3: Insert option ooppn. This yields mooomnpppnon, again lacking any clear structured repetition like mnop or similar. Step 4: Insert option mnooo. This gives mmonmnoponoo, which partially includes mnop but does not reveal a clean repeated pattern. Step 5: Insert option npomp. The completed sequence is mnopmnopmnop. Step 6: We now clearly see that mnopmnopmnop is three consecutive repetitions of the block mnop, a very neat and standard alphabetical pattern.

Verification / Alternative check:
Confirm that mnopmnopmnop is exactly mnop repeated three times. The sequence contains mnop at positions 1 to 4, 5 to 8, and 9 to 12. No other insertion option produces such a clear and symmetric structure. This is exactly the type of pattern that exam setters prefer, confirming that npomp is the correct choice.

Why Other Options Are Wrong:
The sequences generated by mmnno, ooppn, and mnooo either repeat letters in an uneven manner or break an emerging alphabetical flow. They do not correspond to a clean repetition of any natural block like mnop. As a result, they are far less plausible as intended completions. The none of these option is invalid, because npomp yields a perfectly regular series.

Common Pitfalls:
Some students may stop after testing only the first or second option, settling for a sequence that appears complicated but not truly systematic. Others may not think to look for well known patterns like abcd or mnop. Explicitly writing out each completed sequence and then checking for block repetition is a reliable way to avoid mistakes.

Final Answer:
The set of letters that correctly completes the series is npomp, producing mnopmnopmnop.