Gandak, Burhi Gandak, Bagmati, Sikarhana and Lalbakia are important rivers of which district of Bihar.

The correct answer is D. Gaya.

Gandak, Burhi Gandak, Bagmati, Sikarhana and Lalbakia are important rivers of Gaya district in Bihar. The Gandak is a major tributary of the Ganges River. The Burhi Gandak is a tributary of the Gandak River. The Bagmati is a tributary of the Ganges River. The Sikarhana is a tributary of the Bagmati River. The Lalbakia is a tributary of the Sikarhana River.

East Champaran, West Champaran and Kaimur are also districts of Bihar, but they do not have any of these rivers.