The tax benefit rule applies in which of the following situations:

a. The taxpayer receives a refund for overpayment of state taxes paid which the taxpayer deducted in the previous year.

b. The taxpayer receives an insurance reimbursement for a medical expense which the taxpayer deducted in the previous year.

c. The taxpayer receives a partial payment for a business bad debt which he deducted in a prior year.

d. All of the above.