To answer this question, let's go through each option to understand why it is correct or incorrect:
Option A) All actions in a statechart diagram are attached to transitions.
This option is incorrect. While actions in a statechart diagram can be attached to transitions, they can also be attached to states. Actions in a state are executed when an object enters or exits that state, regardless of the triggering event.
Option B) An event may cause an object to remain in the same state it was prior to the event.
This option is correct. In a statechart diagram, an event can occur and cause a transition from one state to another. However, it is also possible for an event to occur and have no effect on the object's state, causing it to remain in the same state it was in prior to the event.
Option C) Once an object leaves a state, it cannot return to that state.
This option is incorrect. In a statechart diagram, an object can enter and exit states multiple times. The statechart allows for transitions that can loop back to a previous state, allowing an object to return to a state it has previously been in.
Option D) Two different transitions out of the same state may overlap (they can be triggered by the same event).
This option is incorrect. In a statechart diagram, two different transitions out of the same state cannot overlap. Only one transition can be triggered by a specific event at a given time.
The correct answer is B) An event may cause an object to remain in the same state it was prior to the event. This option is correct because it acknowledges that an event can occur without causing a state change, allowing the object to remain in the same state.