Select the letter-cluster from among the given options that can replace the question mark (?) in the following series. BCD, EFG, HIJ, ?

Correct — A.
Rule: consecutive letters, three at a time, each cluster starting where the last one stopped.

BCD = 2, 3, 4
EFG = 5, 6, 7
HIJ = 8, 9, 10
Next: 11, 12, 13 = KLM → option (a).

Why the others are wrong

• (b)
  GHS — GHS goes backwards: G sits inside EFG and H inside HIJ. The run has reached J, so the next cluster must start at K.
• (c)
  BHS — BHS restarts at B, the letter the series opened with. Its letters are not even consecutive: B, H, S jump by 6 and 11.
• (d)
  KMN — KMN starts correctly at K but skips L. Each cluster is three letters in a row, so K must be followed by L, then M.

Read the three clusters as one unbroken alphabet: B C D E F G H I J. Cut into groups of three, that gives BCD, EFG, HIJ, so the next group is simply the next three letters, K L M.

A second check is the first letters alone. B, E, H sit at 2, 5, 8, a step of +3, so the next cluster starts at 11, which is K.

Key facts

• B = 2, E = 5, H = 8, K = 11: the clusters start three letters apart.
• E = 5, J = 10, O = 15, T = 20, Y = 25 are quick anchors for counting letter positions.
• K, L, M are the 11th, 12th and 13th letters.

Common traps

• Picking KMN because it starts with K, without checking that L comes next
• Losing count past J: J is the 10th letter, so the next cluster starts at the 11th, K

No directly related past PYQ was found.