Which of the following features would not generally be considered common to alforecasts:

a$.$ Assumption of a stable underlying causal system.

b$.$ Actual results will differ somewhat from predicted values.

c$.$Historical data is availabie on which to base the forecast.

d$.$ Forecast for group of items tend to be more accurate than forecasts for individualitems.

e$.$ Accuracy decreases as the time horizon increases.