The correct answer is Hindi.
Hindi is the official language of Bihar. It is also the most widely spoken language in the state, with over 80% of the population speaking it as their first language. Hindi is a member of the Indo-Aryan language family and is closely related to Urdu. It is written in the Devanagari script.
Marathi and English are also official languages of Bihar. However, they are not as widely spoken as Hindi. Marathi is a Dravidian language spoken by about 10% of the population of Bihar. It is written in the Devanagari script. English is a foreign language that is taught in schools and used in government and business.
Urdu is a Persianized form of Hindi that is spoken by about 1% of the population of Bihar. It is written in the Nastaliq script.
Bangla is a Bengali language that is spoken by about 2% of the population of Bihar. It is written in the Bengali script.