Explanation:

- "Marriage by trial" among the Bhils isn’t just some old custom—it’s a big deal that puts a spotlight on qualities like courage and bravery, which the community really values in young men.

- This trial isn’t random. It’s specifically held during the Mela (Option 1). Mela is more than just a fair—it's a major cultural event for the Bhils. It’s when the whole community gathers, making it a perfect stage for these public trials.

- Option 2, Marriage, is actually the outcome, not the occasion for the trial. The trial happens first.

- Option 3, Holi, is a popular festival, but for the Bhils, marriage by trial isn’t tied to Holi celebrations.

- Option 4, Diwali, is another big festival, but again, this tradition is not practiced then.

- So, the right answer is Option 1: Mela. This is when young men prove their mettle.