Which of the following is true about active states in a region?

• A. Every region has at least one active state
• B. Regions must be active in all states at once
• C. Regions can have zero active states temporarily
• D. Regions require two active states

Answer: (A)

In a state-machine that uses regions, each region represents a separate line of behavior and must be in some substate at any moment. That means there is always at least one active state within every region, giving the system a defined current configuration and enabling transitions to depend on that active state. It’s also typical that within a single region only one substate is active at a time, so the idea isn’t that a region would have multiple active states simultaneously. The other statements conflict with how regions are designed: a region isn’t required to have active states in all its sub-states at once, it isn’t allowed to have zero active states, and it doesn’t require two active states in a region. Therefore, the correct understanding is that every region has at least one active state.