When introducing to a tour group to America about what they should do when encountering any emergencies or other problems, which of the following body structures might the speaker use?
【单选题】Suppose roll the dice repeated continuously three times, let Ai be the event that ith occurrence of one point that the dice shows (i = 1,2,3) , A 1 ∪A 2 ∪A 3 denotes ( ).