It's now or never...

While I was waiting for the optometrist during my yearly eye exam on Monday, Elvis Presley's "It's Now or Never" was playing over the radio. Now before then, if someone had come up to me and asked me to sing it, I would have told them I couldn't. However, while sitting in my chair, I eerily knew the melody Elvis was singing and I could not figure out why... that is until I made the connection that the melody was based on a famous aria. Do you know which one? Answer the question in the poll below.