The correct answer is A. Bank overdraft.
A current asset is an asset that is expected to be realized in cash, sold, or consumed within one year or the operating cycle, whichever is shorter.
Bank overdraft is a short-term loan that a bank allows a customer to take out when their account balance falls below zero. It is a type of current liability, not a current asset.
Closing stock is the value of the goods that a company has left at the end of an accounting period. It is a type of current asset.
Debtors are amounts owed to a company by its customers. They are a type of current asset.
Bills receivable are amounts owed to a company by its customers for goods or services that have been sold on credit. They are a type of current asset.