Explanation:

Let's break this down:

- Levirate is a custom where a man marries his deceased brother’s widow.

- The term "Nantra" is often used in some communities as a synonym for Levirate.

- "Natal" actually refers to something related to birth or native place. It’s not connected to Levirate at all.

- Option 1 says Levirate = Nantra. That’s true in some contexts.

- Option 2 says Levirate = Natal. That’s not correct.

- Option 3 says “Only a” (only Nantra is another word for Levirate). This fits, because “Natal” doesn’t match.

So, the correct answer is Option 1—Levirate is also known as Nantra.

Option 4 is incorrect.