Answer: d. must stop payment if the bank has a reasonable time to act.
Explanation:
Dios as a bank holds money for it's customers which means that the money is still under the ownership of the customer in question to do as they see fit.
If the customer therefore instructs them to act in a certain way with that money, they will do so provided that it is legal of course.
Bok asks Dios to stop a payment related to his own money and so they must do so if they have enough/reasonable time to do so because as their customer, he is there first priority especially in relation to his own money.