The reduced grammar equivalent to the grammar whose production rules are given below is
S → AB | CA
B → BC | AB
A → a
C → aB | b

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.