C is the answer.
https://learn.microsoft.com/en-us/composer/concept-events-and-triggers?tabs=v2x
In Bot Framework Composer, each dialog includes one or more event handlers called triggers. Each trigger contains one or more actions. Actions are the instructions that the bot will execute when the dialog receives any event that it has a trigger defined to handle. Once a given event is handled by a trigger, no further action is taken on that event. Some event handlers have a condition specified that must be met before it will handle the event and if that condition isn't met, the event is passed to the next event handler. If an event isn't handled in a child dialog, it gets passed up to its parent dialog to handle and this continues until it's either handled or reaches the bots main dialog. If no event handler is found, it will be ignored and no action will be taken.