A department records an encumbrance for supplies in the amount of $4,000. The supplies are received in full, together with an invoice for $3,900. The department accepts the supplies. To record this transaction, the department should:

a. reduce encumbrances by $3,900 and record an expenditure of $3,900

b. reduce encumbrances by $4,000 and record an expenditure of $3,900

c. reduce encumbrances by $4,000 and record an expenditure of $4,000

d. reduce encumbrances by $3,900 and record an expenditure of $4,000