Did I answer this correctly? Will thumbs up if correct.

Marissa and Joe are discussing substantive procedures that could be used to help audit an attestation client's purchasing process. Marissa has been tasked with performing substantive procedures in this area and has asked Joe for advice. Which of the following suggestions by Joe represents the most appropriate substantive procedure? Marissa could obtain a test sample of receivables transactions and examine documents corroborating their existence such as bills of lading. Marissa could attempt to obtain written assurances by senior management and the internal audit function attesting to the client's appropriate segregation of duties. Marissa could select a sample of purchase transactions and attempt to trace them back to underlying supporting documents such as purchase orders. None of these answer choices are correct