Which of the following must file Form 1310?

a. The decedent's spouse filing a joint return.

b. The decedent's sister, who is not a court-appointed personal representative and files the final return with a balance due.

c. A court-appointed personal representative filing a return that shows a balance due.

d. The decedent's son, who is not a court-appointed personal representative and files the final return showing a refund.