Explanation:

- Option 1: Year 1991

- Early 1990s, including 1991, were pivotal for economic reforms in India, resulting in significant changes in the banking sector.

- Option 2: Narsimham Committee

- The Narsimham Committee, established in the early 1990s, was crucial for implementing major banking reforms in India, modernizing and making it more competitive.

- Option 3: Y.V. Reddy Committee

- Focused more on financial sectors and public debt, not specifically on broad banking sector reforms.

- Option 4: Only (a) and (b)

- Correctly associates both key factors, 1991 reforms and the Narsimham Committee, with banking sector reforms.

Option 4 is the correct answer.