Select the letter-cluster from among the given options that can replace the question mark (?) in the following series. MNO, JKL, GHI, DEF, ?

Correct — C.
Rule: every letter moves back 3 places from one cluster to the next.

First letters: M(13), J(10), G(7), D(4) → next is A(1).
The same −3 runs through the second letters (N, K, H, E) and the third (O, L, I, F).

DEF − 3 at every position = ABC → option (c).

Why the others are wrong

• (a)
  ASD — ASD starts with the right letter, A, but S and D are not B and C. D, E, F each step back 3 to A, B, C.
• (b)
  CGF — CGF starts with C. The first letters fall M, J, G, D by 3 each time, so the next one is A, not C.
• (d)
  JHB — JHB jumps back up to J, the first letter of the second cluster. The first letters keep falling by 3, so after D comes A.

Turn each letter into its alphabet position (A = 1 … Z = 26) and read the series one position at a time. The first letters run 13, 10, 7, 4, a fall of 3 at each step, and the second and third letters fall by 3 as well.

A shortcut works because every term is three consecutive letters. Find the next first letter and the rest follows: A, then B, C.

Key facts

• D, E, F each minus 3 gives A, B, C.
• A = 1, D = 4, G = 7, J = 10, M = 13 are the first letters here, 3 apart.
• E = 5, J = 10, O = 15, T = 20, Y = 25 are handy reference points for counting positions.

Common traps

• Picking ASD because it starts with the right letter, without checking the second and third letters
• Reading the series as moving forwards because each cluster is in alphabetical order

No directly related past PYQ was found.