When Running an Experiment, Suppose We Assume the Participants in the Experiment

When running an experiment, suppose we assume the participants in the experiment are a random sample of the population. Let Y_i be the outcome for individual i and let D_i equal one if individual i receives the treatment and zero otherwise. What does the assumption of a random treatment imply?

A) $\overline {Y _ { i } \mid D _ { i } = 1}$ - $\overline {Y _ { i } \mid D _ { i } = 0}$ approximates E(Y_i)
B) $\underline { Y _ { i }}$ approximates E(Y_i|D_i = 1) - E(Y_i|D_i = 0)
C) $\overline {Y _ { i } \mid D _ { i } = 1}$ - $\overline {Y _ { i } \mid D _ { i } = 0}$ = 0
D) Selection Bias = 0