The correct answer is: A) Local chieftains.
Naduvazhis were local chieftains who ruled over small territories in Kerala during the Sangam Age. They were often at war with each other, and their power was limited by the strength of their armies. The Naduvazhis were responsible for collecting taxes and maintaining law and order in their territories. They also played a role in religious ceremonies and festivals.
Option B is incorrect because the Naduvazhis were not foreign rulers. They were native to Kerala and ruled over their own people.
Option C is incorrect because the Naduvazhis were not centralized kings. They ruled over small territories and their power was limited.
Option D is incorrect because the Naduvazhis were not religious leaders. They were responsible for collecting taxes and maintaining law and order in their territories. They also played a role in religious ceremonies and festivals, but they were not religious leaders in the traditional sense.