The correct answer is D. Kosi - Magadh.
The Ganga river flows through the following pairs of Administrative Divisions of Bihar:
- Darbhanga - Munger
- Purnea - Bhagalpur
- Tirhut - Saran
The Kosi river flows through the following pairs of Administrative Divisions of Bihar:
- Saharsa - Supaul
- Madhepura - Darbhanga
- Khagaria - Bhagalpur
The Magadh division does not border the Ganga river.