Which one of the following is not a tributary of the river Ganga?

Which one of the following is not a tributary of the river Ganga?

Son
Mahananda
Teesta
Sharada
This question was previously asked in
UPSC CDS-2 – 2016
The Teesta River is a major river that flows through the Indian states of Sikkim and West Bengal and then through Bangladesh before merging with the Brahmaputra River. It is not a tributary of the Ganga River.
Tributaries of the Ganga include major rivers like the Yamuna, Son, Kosi, Gandak, Ghaghara, and Mahananda. The Teesta is a tributary of the Brahmaputra.
The Son River is a major right-bank tributary of the Ganga, flowing from Madhya Pradesh and joining the Ganga in Bihar. The Mahananda River is a left-bank tributary of the Ganga, originating in the Himalayas and flowing through West Bengal before joining the Ganga in Bangladesh. The Sharada River (also known as Kali Ganga or Mahakali) is a tributary of the Ghaghara River, which in turn is a major tributary of the Ganga. Thus, Son, Mahananda, and Sharada are all part of the Ganga river system, while Teesta is part of the Brahmaputra river system.