येरळा ही _____ नदीची उपनदी आहे.

The correct answer is Option A (Krishna).

Key Points:
• Yerala River & Drainage System:
• Yerala is a prominent left-bank tributary of the Krishna River in Maharashtra.
• Origin: It originates in the Mhaskoba hills near Vadgaon in the Solapur/Satara border region and flows predominantly through Satara and Sangli districts.
• Confluence: It merges with the Krishna River from the left bank at Brahmanal in Sangli district.
• Significance: It is one of the few major left-bank tributaries of the Krishna River in Maharashtra (most other tributaries like Koyna, Venna, Warna, and Panchganga join Krishna from the right bank).
• Hence, option (1) Krishna is the correct answer.
• *(Note: In Set C of the official key this question position was marked # due to paper-specific numbering error, but in Set A it is officially confirmed as Option 1)*.
• Key Takeaway: Yerala is a major left-bank tributary of the Krishna river that meets Krishna at Brahmanal (Sangli).