Suppose you have a binary randomized controlled experiment designed to measure the causal effect of X on Y. Let the control group be identified by X​ = 0 and the treatment group by X​ = 1. The differencesofmeans ​estimator, denoted by ​, is an estimator of the causal effect of X on Y because the differencesofmeans estimator​ estimates: A. the change in the expectation of Y as result of an observation being in the treatment group as opposed to the control group. B. the expectation of Y for observations within the control group. C. the expectation of Y for observations within the treatment group. D. All of the above.