In the DFD, the External Entities may be:

In a Data Flow Diagram (DFD), an External Entity (also known as a Terminator, Source, or Sink) represents a person, organization, or system that exists outside the boundaries of the system being modeled but interacts with it. Its fundamental role is to either provide data to the system (acting as a source) or receive data/results from the system (acting as a destination or sink). A single entity can function as both a source and a destination. For example, a 'Customer' entity can submit an 'Order' (source) and later receive a 'Shipment Notification' (destination). Therefore, they are sources of input data or destinations of results.

A. This is incomplete. An external entity can also be a destination (sink) that receives data from the system.
C. This is incomplete. An external entity can also be a source that provides input data to the system.
D. This describes a Data Store, which is a component within the system used to hold data for later access, not an external entity.

1. Hoffer, J. A., George, J. F., & Valacich, J. S. (2014). Modern Systems Analysis and Design (7th ed.). Pearson. In Chapter 6, "Process Modeling," an external entity (termed Source/Sink) is defined as "the origin and/or destination of data; these are sometimes referred to as external entities" (p. 181, Table 6-2).

2. Kendall, K. E., & Kendall, J. E. (2011). Systems Analysis and Design (8th ed.). Prentice Hall. Chapter 7, "Using Data Flow Diagrams," states, "An external entity is a source or destination of data, considered to be external to the system we are studying... An entity may be a source or a destination of data, or both" (p. 194).

3. University of Texas at Austin. (n.d.). MIS 373: Data Flow Diagrams. McCombs School of Business. Retrieved from a course module on Systems Analysis and Design. The materials define an external entity as a "person, organization, organization unit, or system that is external to the system, but interacts with it" and explicitly labels them as "sources and destinations of data."