Choice "B" is correct. The budgetary control account (open purchase orders) represents a portion of the budgetary control balance that has been segregated for expenditure on vendor performance, usually being goods ordered but not yet received. Remember the entry to record a purchase order:

Likewise, the encumbrance balance represents purchase orders outstanding. For the budgetary control (open purchase orders) to exceed the encumbrance balance, a recording error must have been made.Choice "d" is incorrect. Encumbrances represent purchase orders for which the goods ordered are not yet received. Vouchers payable represent the amounts owed and not yet paid for goods received. The relative balances of these accounts have no impact on the balance in the budgetary control account.Choice "a" is incorrect. The budgetary control account is a budgetary account indicating the outstanding purchase orders for goods not yet received. Likewise, the encumbrance balance represents purchase orders outstanding. An excess of purchase orders over invoices received would not explain the difference between these two accounts.Choice "c" is incorrect. Appropriations are recorded when the budget is adopted and are unrelated to encumbrances.