What is uncertainty?

A、Uncertainty is that a kind of behavior would result in two or more than two consequences.;

B、Uncertainty is that a kind of behavior would result in two or more than two consequences that people can not know exactly in advance.;

C、Uncertainty is that a kind of behavior would result in two consequences.;

D、Uncertainty is that a kind of behavior would result in two consequences that people can not know exactly in advance.