The correct answer is (c), Kosi.
The Ramganga is a river in India that flows through the states of Uttarakhand and Uttar Pradesh. It is a tributary of the Ganges River. The Ramganga originates in the Garhwal Himalayas and flows south through the Kumaon Himalayas. It joins the Ganges River near Kanpur.
The Lisar is a river in India that flows through the states of Uttarakhand and Uttar Pradesh. It is a tributary of the Ramganga River. The Lisar originates in the Garhwal Himalayas and flows south through the Kumaon Himalayas. It joins the Ramganga River near Nainital.
The Gangan is a river in India that flows through the states of Uttarakhand and Uttar Pradesh. It is a tributary of the Ramganga River. The Gangan originates in the Garhwal Himalayas and flows south through the Kumaon Himalayas. It joins the Ramganga River near Haldwani.
The Kosi is a river in India that flows through the states of Bihar and Jharkhand. It is a tributary of the Ganges River. The Kosi originates in the Himalayas and flows east through the Bihar plains. It joins the Ganges River near Bhagalpur.
The Kosi is not a tributary of the Ramganga River.