2.C.: Trajectories and probability
An example of classical motion, a ball bouncing between two walls:
If our class would measure the position of the moving ball, the probability distribution of their measurements would change with time:
The center of the probability distribution traces out the trajectory of the particle predicted by classical mechanics. This is important! It is the crucial connection between probability and the laws of mechanics.
In classical mechanics the width of the probability distribution is all due to experimental error. This is not so in quantum mechanics. In quantum mechanics there is a fundamental limit to the precision of a measurement.
No matter how much care and equipment is invested in the experiment, under the laws of quantum mechanics the width of the probability distribution can never be made less than a fundamental limit. This is the uncertainty principle of quantum mechanics.