The headquarters of Bihar State Road Transport Corporation is located in Patna. It is a state-owned corporation that provides road transport services in Bihar. The corporation was established in 1962 and has its headquarters at Patna Bus Stand, Patna. It has a fleet of over 10,000 buses and operates over 1,000 routes in the state. The corporation provides services to both passengers and goods. It also has a number of workshops and depots across the state.
Option A is the correct answer.
Option B is incorrect because Begusarai is a city in Bihar, but it is not the headquarters of the Bihar State Road Transport Corporation.
Option C is incorrect because Kaimur is a district in Bihar, but it is not the headquarters of the Bihar State Road Transport Corporation.
Option D is incorrect because Gaya is a city in Bihar, but it is not the headquarters of the Bihar State Road Transport Corporation.