The best document for an IS auditor to use in detecting a weakness in segregation of duties is a process flowchart. A process flowchart is a diagram that illustrates the sequence of steps, activities, tasks, or decisions involved in a business process. A process flowchart can help detect a weakness in segregation of duties by showing who performs what actions or roles in a process, and whether there is any overlap or conflict of interest among them. The other options are not as useful as a process flowchart in detecting a weakness in segregation of duties, as they do not show who performs what actions or roles in a process. A system flowchart is a diagram that illustrates the components, functions, interactions, or logic of an information system. A data flow diagram is a diagram that illustrates how data flows from sources to destinations through processes, stores, or external entities. An entity-relationship diagram is a diagram that illustrates how entities (such as tables) are related to each other through attributes (such as keys) in a database. References: CISA ReviewManual (Digital Version), Chapter 3, Section 3.2