Which of the following statements about cultural diversity in India are correct?
I. India is characterized by significant cultural diversity, including linguistic, religious, and regional variations.
II. The Indian state has always followed a strict assimilationist policy, suppressing all forms of cultural difference.
III. The concept of "unity in diversity" acknowledges and celebrates cultural differences within a unified nation.
IV. Communalism, regionalism, and casteism pose challenges to the harmonious coexistence of diverse communities.