Explanation:

- Todas: A pastoral tribe from the Nilgiri Hills in India. They are known for their unique culture and traditions. Avoidance practices might not specifically focus on brother-sister relations.

- Nuers: An ethnic group from South Sudan known for their cattle-herding lifestyle. They have distinct social practices, including various avoidance customs.

- Veddas of Ceylon: Indigenous people of Sri Lanka with a rich cultural heritage. Their social structure may have different traditional rules, not explicitly focused on sibling avoidance.

- Andaman Islanders: Indigenous tribes from the Andaman Islands, each with unique cultural practices, not specifically highlighted in brother-sister avoidance by Pritchard.

Option:2, Nuers is the correct answer.