In state machine diagrams, which notation indicates a composite state has nested substates?

• A. Round-Angle with Nested Substates
• B. Round-Angle
• C. Square
• D. Diamond

Answer: (A)

The main idea here is recognizing when a state is composite, meaning it contains other substates inside it. In state machine diagrams, a state drawn as a round-cornered rectangle that explicitly shows nested substates inside its boundary signals a composite state. That round-angle with nested substates communicates that there’s internal structure and behavior grouped under a single parent state, with transitions that occur among the inner substates or through entry/exit points of the composite.

That’s why this notation is the best choice: it directly indicates nesting and hierarchy within the state. A round-angle alone would just be a simple state with no internal states shown. A square doesn’t convey a standard state-type in UML diagrams for nesting, and a diamond is a decision/branch point, not a container for substates.