Final answer:
The correct answer is option a, activity diagram. In software engineering, concurrency is represented using concurrent nodes in an activity diagram.
Step-by-step explanation:
The correct answer is option a, activity diagram.
In software engineering, concurrency refers to the ability of a system to execute multiple tasks simultaneously.
An activity diagram, within the Unified Modeling Language (UML), can be used to represent concurrency by using concurrent nodes. Concurrent nodes are represented by two or more outgoing flows from a single activity node, indicating that multiple activities can occur in parallel.
For example, in an activity diagram representing a banking system, you may have separate concurrent nodes for verifying a customer's account balance and updating transaction records.