In the following question, which one set of letters when sequentially placed at the gaps in the given letter series shall complete it?M _ Q _ C _ M _ Q _ C M

Let's look for a repeating pattern by counting the total number of letters including the gaps. The total length is 12.Let's divide the series into groups of 3:M _ Q | _ C _ | M _ Q | _ C MBy comparing the first group (M _ Q) and the third group (M _ Q), they are identical.By comparing with the other positions, we can deduce a repeating pattern of 3 letters: M Q CLet's fill the blanks to form "M Q C" repeatedly:1st blank: Q $\to$ M Q Q (Wait, if the pattern is M Q C, then 1st group is M Q C $\to$ blank is C)Let's test the pattern M Q C:Group 1: M C Q (Doesn't fit M Q C)Let's test a repeating pattern of 4 letters: M _ Q _ | C _ M _ | Q _ C MIf the block is M Q C M:1st block: M Q Q C (No)Let's look closely at the choices to find the correct fit:If we use option B (C, Q, M, C, Q):Series becomes: M C Q Q C M M C Q Q C MGrouping by 6: M C Q Q C M | M C Q Q C MThis forms a perfectly repeating 6-letter pattern: M C Q Q C M.Let's double check the blanks filled by option B:1st blank: C2nd blank: Q3rd blank: M4th blank: C5th blank: QThe filled series is exactly M C Q Q C M M C Q Q C M. Thus, option B is correct.