Final answer:
The Stacking rule in an activity diagram allows an action represented by a rectangle to be replaced by two rounded-edge rectangles. This rule facilitates the representation of complex actions that might be broken down into sub-actions within a diagram. It aligns with the concept of replacing one solution with another in a design context.
Step-by-step explanation:
The correct answer to the question regarding an activity diagram in a software design context is C) Stacking. The Stacking rule specifies that any rectangle, which typically represents an action in an activity diagram, can be replaced by two rounded-edge rectangles. This is similar to conceptually replacing a square peg that fits through a square hole with a round peg that fits through a round hole, a metaphor often used to illustrate when one solution can be substituted for another.
To modify the diagram to depict this effect, you would start by drawing the initial action as a rectangle, and then you would split this action into two separate actions, representing each with a rounded-edge rectangle. In the context of Venn diagrams or other probability representations, you would draw a rectangle to represent the sample space and then draw circles or ovals inside to represent events of interest, like belonging to a club (C) and working part time (PT), with overlapping areas indicating joint membership in both events.
To describe areas in a Venn diagram, for example, the area in the rectangle but outside both the circle and the oval, one would use a complete sentence to articulate what that area represents--such as, "This area represents members of the sample space who neither belong to the club nor work part-time."