Which part of Bihar is known as Bhangar soil area?

• A. Areas of West Champaran, Nalanda, Gaya and Sahasram
• B. Areas of Gaya, Nalanda, Bodh Gaya and Sahasram
• C. Area of ​​Purnia, Darbhanga, Saharsa, Muzaffarpur
• D. Area of ​​Gaya, Bodh Gaya, East Champaran and Bhagalpur