According to the ArchiMate language structure, a concept is either an element or a relationship. An element is either a behavior element, a structure element, a motivation element, or a composite element. A and B in the diagram correspond to these concepts respectively.

Based on the ArchiMate 3 documents or objectives, the generic metamodel defines two main types of elements: structure and behavior. Structure elements represent the structural concepts that model the static construction or composition of concepts of the same or different types. Behavior elements represent units of activity performed by one or more active structure elements.

According to the physical elements metamodel, a facility is a specialization of a node, which is an active structure element that represents a computational or physical resource that hosts, manipulates, or interacts with other computational or physical resources. A facility can be used to model physical buildings or locations.

According to the ArchiMate 3.2 Specification1, external active structure elements are also called interfaces. An interface represents a point of access where one or more services are offered by an active structure element to its environment1. Therefore, the correct answer is B. Interfaces.