To infer that an intervention is the real cause of a change:
a.
we must make sure that the change preceded the onset of the intervention
b.
it is sufficient to know that the intervention is correlated with the change.
c.
we must ascertain whether the change is correlated with the intervention, learn that it did not precede the intervention, and eliminate plausible alternative explanations for the change.
d.
rely on studies that avoided the use of random assignment to treatment conditions.