设<img src="https://static.zxtiku.com/wangke/imgs/topic/09d337a26b537a3dfa49699fb8266c02.png"/> 是两个事件,且<img src="https://static.zxtiku.com/wangke/imgs/topic/2ccbebdae52d18c67874e7a409e73cb6.png"/> ,则A和B的关系一定是()