D is correct. The EWMA estimate of variance is a weighted average of the variance rate estimated for the prior day and the prior day's observed squared return. A is incorrect. EWMA is a particular case of GARCH (1,1) with the weight assigned to the long-run average variance rate as zero and the sum of the weights of the other two parameters equal to 1. B is incorrect because there is also weight assigned to the long-run average variance rate. C is incorrect because such a comparison can only be done under specific parameter configurations.