Consider the sequence AB_CC_A_BCCC_BBC_C that follows a certain pattern. Which one of the following completes the sequence ?

(a) B, C, B, C, A
(b) A, C, B, C, A
(c) B, C, B, A, C ✓ UPSC's answer
(d) C, B, B, A, C

Why the answer is (c)

• The sequence has 18 positions, with blanks at positions 3, 6, 8, 13 and 17.

• The visible letters fit a repeated 6-letter block ABBCCC: positions 1-2 are AB, positions 4-5 are CC, position 7 is A, positions 9-12 are BCCC, positions 14-16 are BBC, and position 18 is C.

• Completing three ABBCCC blocks requires position 3 = B, position 6 = C, position 8 = B, position 13 = A, and position 17 = C.

• This gives ABBCCC ABBCCC ABBCCC, which matches every given letter.

• Therefore option (c) B, C, B, A, C completes the sequence.

Why the other options are wrong

(a) B, C, B, C, A: Option (a) makes position 13 C and position 17 A, so the final block is not ABBCCC.
(b) A, C, B, C, A: Option (b) makes position 3 A instead of B, so the first block is not ABBCCC.
(d) C, B, B, A, C: Option (d) makes position 3 C and position 6 B, so the first block is not ABBCCC.

Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2025, held on 25 May 2025. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.