Regarding the statute of limitations on additional assessments of tax by the IRS, select the applicable date in each of the following situations.

Note: Assume a calendar year individual with no fraud or substantial omissions involved.

a. The income tax return for 2018 was filed on January 31, 2019. The three-year statute of limitations will begin to run on .

b. The income tax return for 2018 was filed on December 1, 2019. The statute of limitations will begin to run on .

c. The income tax return for 2018 was prepared on April 1, 2019, but was never filed. Through some misunderstanding between the preparer and the taxpayer, each expected the other to file the return. The statute of limitations .

d. The income tax return for 2018 was never filed because the taxpayer thought no additional tax was due. The statute of limitations .