The reduced grammar equivalent to S → AB | CA, B → BC | AB, A → a, C → aB | b is

1. AS → CA, A → a, C → b
2. BS → CA | B, B → BC | B, A → a, C → aB | b
3. CS → CA | B, B → BC, A → a, C → aB | b
4. DS → AB | AC, B → BC | BA, A → a, C → aB | b

Pick an option to check yourself, or open the answer below.

Show answer & explanation

Correct answer: A. S → CA, A → a, C → b

Explanation

Every B-production contains B again, so B never derives a terminal string: B is useless. Removing it (and S → AB, C → aB) leaves S → CA, A → a, C → b.