Multiple-Treatment Interference Refers to the Situation in Which

Multiple-treatment interference refers to the situation in which

A) research participants' performance on the dependent variable reflects the combined effect of more than one treatment.
B) extraneous variables rather than the experimental treatment are responsible for the experimental outcome.
C) high correlations between pretest and posttest scores reduce the chances of significant gain scores.
D) research participants in the control group are affected by their knowledge of the experimental treatment.