The answer is All-A, B, C, D, E, and F.
Every RCA is practically a drill down exercise which means the necessity of the presence of sufficient triggers is responsible for the event to occur.
Just like a pull system, only if 'An' is present will the consecutive step/activity be triggered. It is a chain of events which can be broken down only after removal/handling of the primary root cause.
Regards,
Dr. Bhamini Thukral