Which of the following is one of Asia's largest cattle fairs, organized at the confluence of two mighty rivers, the Ganga and Gandak?

The correct option is Sonepur Fair.

Step-by-step Explanation:
1. Sonepur Cattle Fair: Held on Kartik Poornima (the full moon day) in the month of November in Sonepur, Bihar, the Sonepur Fair (also known as Harihar Kshetra Mela) is one of Asia's largest cattle fairs.
2. Geographical Significance: The fair takes place at the confluence of the sacred rivers Ganga (Ganges) and Gandak (also known as Narayani).
3. Cultural Importance: It draws pilgrims and visitors from all across Asia for holy dips at the confluence and for trading a wide variety of domestic animals including cattle, horses, and camels.

Overview of Other Options:
• Suraj Kund Craft Mela: Held annually in Faridabad, Haryana, celebrating international crafts and handicrafts.
• Flamingo Festival: Celebrated at the Pulicat Lake and Nelapattu Bird Sanctuary in Andhra Pradesh.
• Thrissur Pooram: A famous annual temple festival held in Thrissur, Kerala.