बिहार में सिंचाई का सबसे प्रमुख साधन क्या है ? - What is the main means of irrigation in Bihar? - Bihar Me Irrigation Ka Sabse Pramukh Sadhan Kya Hai ? Bihar Gk in hindi, Drainage System NalKoop question answers in hindi pdf Talab questions in hindi, Know About Nahar Bihar Gk online test Bihar Gk notes in hindi quiz book Kuaan