Rivers belonging to which one of the following groups form the boundary between Bihar and Uttar Pradesh?

The correct answer is C. Karmanasa, Gandak and Ghaghra.

The Karmanasa, Gandak and Ghaghra are rivers that form the boundary between Bihar and Uttar Pradesh. The Karmanasa is a tributary of the Ganges River, and it flows through the states of Bihar and Uttar Pradesh. The Gandak is a tributary of the Ganges River, and it flows through the states of Bihar, Jharkhand and Uttar Pradesh. The Ghaghra is a tributary of the Ganges River, and it flows through the states of Uttar Pradesh, Bihar and Nepal.

The other options are incorrect because they do not include all three rivers that form the boundary between Bihar and Uttar Pradesh. Option A includes the Kamla, Son and Baghmati rivers, but it does not include the Karmanasa, Gandak or Ghaghra rivers. Option B includes the Budi Gandak, Kosi and Ganga rivers, but it does not include the Karmanasa, Gandak or Ghaghra rivers. Option D includes the North Koel, Ajay and Punpun rivers, but it does not include the Karmanasa, Gandak or Ghaghra rivers.