Option 1 -> Temples and natural beauty are mentioned but temples "fostered" the arts rather than being the primary factor responsible for cultural heritage.
Option 2 -> Traditions and simplicity are discussed about folk people, but not specifically identified as the factor responsible for Tamilnad's cultural heritage.
Option 3 -> The passage explicitly states "folk arts, culture and tradition had a great part to play in the development of these [arts and cultural elements]."
Option 4 -> These are the outcomes/expressions of cultural heritage (what the temples fostered), not the factors responsible for it.
Hence, Option 3: folk art, culture and tradition -> The passage clearly mentions that folk arts, culture and tradition played a great part in the development of Tamilnad's magnificent temples and associated arts like architecture, sculpture, music, dance, painting and literature, making them a key factor responsible for the region's cultural heritage -> correct