Question: 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.
Please eliminate two incorrect options first, then think it step by step and choose the most proper one option.