Which of the following forms cannot be electronically amended using Form 1040-X?

Form 1040-X, the Amended U.S. Individual Income Tax Return, allows taxpayers to correct errors or make changes to previously filed tax returns. However, it is important to note that electronic amendment capabilities are limited to certain forms and tax years.

Forms 1040-A were phased out after the tax year 2017, with the last allowable filers needing to transition to the standard Form 1040 starting in tax year 2018. This means that any filing prior to this date using Form 1040-A cannot be electronically amended because the IRS no longer supports electronic filing for that specific form. Taxpayers must resort to a paper amendment process for any corrections needed on those older filings.

In contrast, the other forms listed (including recent versions of Forms 1040 and 1040-NR for the appropriate years) can be amended electronically, allowing taxpayers to efficiently correct any mistakes or make changes without the need for paper submissions. Therefore, 1040-A forms stand out as ineligible for electronic amendments, which directly leads to the identification of the correct choice.