Explanation:

Let’s break it down:

- Jamnagar (Option 1) is home to the world's largest oil refinery, but it started operations in 1999. That’s pretty new in refinery terms.

- Paradip (Option 2) is an even newer refinery, commissioned by Indian Oil in 2016.

- Digboi (Option 3) is the oldest operating refinery in India—and actually one of the oldest in the world. It began production all the way back in 1901, up in Assam. That’s more than a century old, still chugging along.

- Panipat (Option 4) opened much later, in the 1990s.

So yes, Digboi is the real deal here.