Question

In a double blind experiment, which of the following is true?
A. the experimenter does not know which subjects are in the treatment group.
B.the experiments conducted in a specially darkened and soundproof room to eliminate the influence of chance enviromental variables.
C.neither the subjects nor the experimenter know who is in the treatment group
D.the subjects are not told the purposr of the experiment
E.each ex[erimental subject is assigned to exactly two blocks