Is It Possible to Establish the Probability of an Event

Is it possible to establish the probability of an event that has already occurred?

A) No, because by its very nature, probability only applies to future events.
B) No, because after an event has occurred, we can't determine what all of the other possible outcomes might have been.
C) Yes, since we could still determine how likely the outcome was, relative to the other outcomes that might have occurred.
D) Yes, but we can only consider the probability to be 1, since the event definitely happened.
E) Yes, but the probability cannot be established as precisely as it could have been before the event occurred.