Explanation:

- The term "twice-born" refers to the concept of undergoing a spiritual rebirth or initiation.

- In Hindu tradition, this applies to the three higher varnas who undergo the Upanayana ceremony.

- Brahmins (Option 1): Priestly class who perform religious rituals.

- Kshatriyas (Option 3): Warrior and ruler class, responsible for protection and governance.

- Vaishyas (Option 2): Merchant and farmer class, engaged in trade and agriculture.

- The Shudras, the fourth varna, are not considered "twice-born."

- Therefore, "twice-born" applies to Brahmins, Kshatriyas, and Vaishyas.

- Answer: Option 4 - All of the above is correct.