Which of the following is both a necessary and a sufficient principle to prove a causal relationship?

a. Where there is the effect, there must also be the cause.
b. Where there is no cause, there should be no effect.
c. Where there is a change made in the cause, there should be a resulting change in the effect.
d. All of these are necessary and sufficient conditions for proving a causal relationship between variables.

C
The first two principles are true for events that are correlated but not causally related. They are necessary but not sufficient for proving causality.