An auditor observes the mailing of monthly statements to a client's customers and reviews evidence of follow-up on errors reported by the customers. This test of controls most likely is performed to support management's financial statement assertions of

Answer: Rights and obligations

Explanation:

According to the given question, an auditor is basically observe the monthly statement of the customer and the client reviews on the behalf of given evidences and also the reported errors by the users.

The controlling process is basically performed by the financial management of the rights and the obligation assertions.

The rights and obligation of assertion is one of the type of basic assertion type which basically include all the liability and assert of an organization in the form of financial statement. It basically state the legal right of the company and the process of using these rights in the business.

Therefore Rights and obligations is the correct answer.