Demarcus is a sole proprietor who had a nonfarm net operating loss in 2020. Which of the following is not an option for his loss?

a. Demarcus may waive the carryback by attaching a statement to his timely filed 2020 return

b. He may carry the loss back to his 2015 return using Form 1040X

c. He may carry the loss back to his 2015 return using Form 1045

d. He may carry the loss back to his 2015 return using Form 1139