Consider the following sequence that follows some arrangement:
c_accaa_aa_bc_b
The letters that appear in the gaps are
Answer & explanation
Answer: (b) cbbb
With c, b, b, b the series reads ccacc | aabaa | bbcbb — three five-letter blocks, each of the form x x y x x. No other option keeps this shape.
- The series has 15 places; split into blocks of five: c _ a c c | a a _ a a | _ b c _ b.
- Each block has the shape x x y x x: c c a c c needs c; a a b a a needs b.
- The third block b b c b b needs b in both gaps.
- Gaps in order: c, b, b, b.
- Check: option (a) would make the first block c a a c c, which breaks the pattern.
Remember · For letter-gap series, split the string into equal blocks (4, 5 or 6 letters) and look for a repeating shape.
Question and answer: UPSC's official GS Paper II (2019, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·