Which of the Following Is an Example of an Independent

Which of the following is an example of an independent check on performance?

A) Every year, Doug is required to take one full week of vacation time.
B) Greg is in charge of recording receipt of payments made to accounts receivable, while Susan is in charge of making deposits to the bank.
C) Every evening, Shellie makes a back-up file of all transactions recorded in the computer that day, burns the back-up file onto a CD and then locks the CD into a fire-proof vault for the night.
D) John, a clerk, is authorized to perform transactions as large as $5,000 but must maintain authorization from Andrea to perform larger transactions.