How does a randomized controlled trial work in assessing the effectiveness of therapy?

How does a randomized controlled trial work in assessing the effectiveness of therapy?
a)  People with a given disorder are randomly assigned to one or more treatment groups or to a control group.
b)  Best clinical practices are codified in a kind of "handbook," and clinicians who adopt that therapeutic perspective are encouraged to follow that guide.
c)  Psychological scientists review a random selection of case notes on an anonymous client, where the parameters of a disorder have been carefully controlled ahead of time.
d)  Clinicians' case notes, representing different perspectives on a single case, are reviewed by a panel of qualified mental health professionals to judge the best outcomes.