Caste has NOT spread into which of the following non-Hindu communities of Indian sub-continent?

None of the above

The correct answer is Option 4: None of the above

NCERT: Caste is an institution uniquely associated with the Indian sub-continent. While social arrangements producing similar effects have existed in other parts of the world, the exact form has not been found elsewhere. Although it is an institution characteristic of Hindu society, caste has spread to the major non-Hindu communities of the Indian sub-continent. This is specially true of Muslims, Christians and Sikhs.