Blanche filed her 2016 income tax return on April 4, 2017. On December 14, 2017, she learned that 100 shares of stock that she owned had become worthless in 2016. Because she did not deduct this loss on the 2016 return, Blanche intends to file a claim for refund. This claim must be filed by no later than April 15 of what year?

a. 2018

b. 2021

c. 2023

d. 2024

e. There is no expiration date for the statute of limitations in this context.