In One-Factor Repeated Measures Model, Scores Are Collected at Three

In one-factor repeated measures model, scores are collected at three different time points (J = 3) . The assumption of sphericity basically states that

A) The variance of scores collected at each time point is the same.
B) The variance of the difference scores between the first time point and the second time point is the same as that between the second time point and the third time point.
C) The variance of the difference scores is the same for each of the three pairs of time points.
D) Both the variance and covariance of the difference scores are the same for each of the three pairs of time points.