The correct answer is A. Patna.
Patna is the capital of Bihar and the headquarters of the Bihar Police. The Bihar Police is a state police force responsible for law enforcement and public safety in the state of Bihar. The Bihar Police is headed by the Director General of Police (DGP), who is appointed by the state government. The DGP is assisted by a number of Additional Director Generals (ADGPs), Inspector Generals of Police (IGPs), and Deputy Inspector Generals of Police (DIGs). The Bihar Police is divided into a number of districts, each of which is headed by a Superintendent of Police (SP). The SP is assisted by a number of Deputy Superintendents of Police (DSPs), Inspectors, Sub-Inspectors, and Constables. The Bihar Police is responsible for a wide range of duties, including maintaining law and order, investigating crimes, and providing security to the public.
Ranchi is the capital of Jharkhand and is not the headquarters of the Bihar Police. Muzaffarpur is a city in Bihar and is not the headquarters of the Bihar Police.