A demand forecasting system uses Holt-Winters with optimized smoothing parameters. Consider the following statements.

I. A high α generally makes the level component more responsive to recent observations.

II. A low β guarantees that future forecasts will have almost no trend.

III. A low γ makes the seasonal component update more slowly.

IV. Optimizing α, β and γ guarantees the lowest possible RMSE on the test dataset.

Which statements are correct?