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

Correct — C.
Rule: the alphabet in blocks of three, each block starting 3 letters after the last.

Starts: J(10), M(13), P(16) → next start S(19).
Each cluster is three letters in a row: J K L, M N O, P Q R.
So the next cluster is S T U → option (c).

Why the others are wrong

• (a)
  SFD — SFD starts correctly at S but then jumps back to F and D. The block after P Q R is three letters in a row: S T U.
• (b)
  BHF — BHF starts at B, far behind P. The first letters climb J, M, P in threes, so the next must be S.
• (d)
  DTG — DTG starts at D, not S, and its letters are not consecutive. Each given cluster is three letters in a row.

Read the series one column at a time. First letters J, M, P, S. Second letters K, N, Q, T. Third letters L, O, R, U. Every column climbs by 3.

Because each cluster is itself three consecutive letters, a +3 start means the clusters tile the alphabet: J through U with no letter skipped and none repeated.

Key facts

• J = 10, M = 13, P = 16, S = 19.
• Blocks of three consecutive letters that start 3 apart cover the alphabet with no gap and no overlap.
• The block after P Q R is S T U.

Common traps

• Choosing SFD because its first letter is right

No directly related past PYQ was found.