When the underlying mean of a time series is very stable and there are no trend, cyclical, or ...

When the underlying mean of a time series is very stable and there are no trend, cyclical, or seasonal influences:
 
  A) a simple moving-average forecast with n = 20 should outperform a simple moving-average forecast with n = 3.
  B) a simple moving-average forecast with n = 3 should outperform a simple moving-average forecast with n = 15.
  C) a simple moving-average forecast with n = 20 should perform about the same as a simple moving-average forecast with n = 3.
  D) an exponential smoothing forecast with a = 0.30 should outperform a simple moving-average forecast with  = 0.01.