According to tradition, the Mahabharata was recited in public for the first time at the occasion of great sacrifice held by:

Correct option is A

The Mahabharata was first publicly recited at the great snake sacrifice (Sarpayajna) held by King Janamejaya.

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King Janamejaya was the great-grandson of Arjuna and the son of King Parikshita.
Janamejaya organized the Sarpayajna to avenge the death of his father, King Parikshita, who was killed by the snake king Takshaka.
It was at this sacrifice that the sage Vaisampayana, a disciple of the original compiler Vyasa, first recited the entire narrative of the Mahabharata to King Janamejaya.
This recitation is known as the Jaya (Victory) recitation. The version generally studied today is the one later narrated by Suta Ugrashravas to a gathering of sages in the Naimisha Forest.