Of the Following Statements About an Internal Control, Which One

Of the following statements about an internal control, which one is not valid?

A) No one person should be responsible for the custodial responsibility and the recording responsibility for an asset.
B) Transactions must be properly authorised before such transactions are processed.
C) Because of the cost-benefit relationship, a client may apply control procedures on a test basis.
D) Control procedures reasonably ensure that collusion among employees cannot occur.