Hollis and Arlene are married and filed a joint return on April 15, 20x1 but then realized they incorrectly reported Arlene's income. Per the statute of limitations, by what date do they have to file an amended return?

December 31, 20x1

April 15, 20x2

April 15, 20x4

They can file at any time as long as fraud was not committed when preparing the original return