Task: Question Answering
Input (English): Which of the following is a true statement?
(A)While observational studies gather information on an already existing condition, they still often involve intentionally forcing some treatment to note the response. (B)In an experiment, researchers decide on the treatment but typically allow the subjects to self-select into the control group. (C)If properly designed, either observational studies or controlled experiments can easily be used to establish cause and effect. (D)Stratifying in sampling is the same idea as blocking for experiments.
Output (English): D