The correct answer is D. Petty Cash Book.
An imprest system is a system of cash management in which a fixed amount of money is set aside for small expenses. This amount is called the imprest fund, and it is typically kept in a petty cash box. When an employee needs to make a small purchase, they can draw money from the petty cash box and then submit a receipt for reimbursement.
The imprest system is a good way to control small expenses because it helps to ensure that only authorized employees have access to the petty cash fund. It also helps to track expenses, as all receipts must be submitted for reimbursement.
The other options are incorrect because they are not used in relation to an imprest system.
A purchase book is a book that is used to record purchases of goods and services. A sales book is a book that is used to record sales of goods and services. A cash book is a book that is used to record all cash transactions, both receipts and payments.