d. a letter to a customer denying a request for credit.
Routine messages are part of a business' daily operations; It communicates the what, who, where and when elements of operations. They are usually simple and positive requests for information or action by one person to another, daily meeting with coworkers, new updates and instructions as well as replies to customers. Among the choices given, a letter to a customer denying a request for credit is not part of it.
