The correct answer is: a) Ganga, Kosi, and Gandak.
The major canal systems in Bihar draw water from the rivers Ganga, Kosi, and Gandak. These rivers are all located in the northern part of India and are major sources of water for irrigation and drinking water. The Ganga is the longest river in India and is also one of the most sacred rivers in Hinduism. The Kosi is a major tributary of the Ganga and is known for its destructive floods. The Gandak is another major tributary of the Ganga and is a major source of water for irrigation in Bihar.
The other options are incorrect because they do not include the rivers Ganga, Kosi, and Gandak. The Brahmaputra is a major river in northeastern India and is not a major source of water for Bihar. The Son is a major river in central India and is not a major source of water for Bihar. The Mahananda is a major river in West Bengal and is not a major source of water for Bihar. The Yamuna, Chambal, and Narmada are all major rivers in central India and are not major sources of water for Bihar. The Krishna, Godavari, and Cauvery are all major rivers in southern India and are not major sources of water for Bihar.