Concept:Bhagalpur is widely recognized as the 'silk city' of Bihar due to its historical and leading role in silk production and handloom weaving.
Explanation:Bihar has over 90,000 weavers, with Bhagalpur being the most prominent silk centre.
Other weaving centres like Gaya have around 8,000 weavers, but Bhagalpur remains the leading silk hub.
Traditional handloom clusters are also found in Gaya, Nalanda, Darbhanga, Madhubani, Siwan, and Patna, but none are called the 'silk city'.
Infrastructure Leasing and Financial Services has prepared reports for textile parks, yet most textile centres in the state are declining and produce low-value goods.
Gaya is growing fast in textiles with about 10,000 looms, but it does not hold the title of 'silk city'.
Therefore, the district known as 'silk city' is Bhagalpur.
Answer:B. Bhagalpur