The correct answer is B. BSNL.
BSNL is a state-owned telecommunications company in India. It is the largest telecommunications service provider in India, with a subscriber base of over 270 million. BSNL offers a wide range of services, including voice, data, and internet services. It has a presence in all 29 states and 7 union territories of India.
Airtel is a multinational telecommunications company headquartered in New Delhi, India. It is the second largest mobile network operator in India, with a subscriber base of over 350 million. Airtel offers a wide range of services, including voice, data, and internet services. It has a presence in over 20 countries across Asia, Africa, and Europe.
Reliance Jio Infocomm Limited is an Indian multinational telecommunications company headquartered in Navi Mumbai, Maharashtra. It is the third largest mobile network operator in India, with a subscriber base of over 300 million. Reliance Jio offers a wide range of services, including voice, data, and internet services. It has a presence in all 29 states and 7 union territories of India.
Idea Cellular is an Indian multinational telecommunications company headquartered in Mumbai, Maharashtra. It is the fourth largest mobile network operator in India, with a subscriber base of over 250 million. Idea Cellular offers a wide range of services, including voice, data, and internet services. It has a presence in all 29 states and 7 union territories of India.
In conclusion, BSNL is the only public telecommunication service provider that covers all the 38 districts of Bihar.