Explanation:

- Ustad Amir Khan was a renowned Indian classical vocalist known for his unique and intellectual approach to Hindustani music.

- Option 1: Gwalior

- The Gwalior Gharana is one of the oldest Khayal gharanas known for its traditional and methodical style.

- Option 2: Indore

- The Indore Gharana was founded by Ustad Amir Khan himself. It emphasizes slow tempo, intricate melodic patterns, and emotional depth.

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- Option 3: Maihar

- The Maihar Gharana is famous for instrumental music and was popularized by Allauddin Khan. It’s not related to Amir Khan's vocal tradition.

- Option 4: Bhopal

- Bhopal is not traditionally recognized as a major gharana in Hindustani classical music.

Ustad Amir Khan's contribution to the Indore Gharana is significant, offering a distinctive style and profound impact on subsequent generations.