Answer:
Correct order is:
2. A civilization emerged in the Indus Valley.
1. Rituals such as fire sacrifices began.
3. Scholars wrote the Rig Veda.
Explanation:
According to the historical sources that we have first civilization in the Indus Valley appeared somewhere around 3300 BC.
Rituals mentioned in here appeared in the Vedic period, or probably even before.
Therefore the Rig Veda were the last in this order, as they were written somewhere in the middle of 2nd Millennium BC.
