Consider the following techniques of transforming time series data. Choose all that apply

3. Fitting a regression model of the series on a periodic function (e.g. sine wave of a fixed period) of the time index and subtracting off the fitted model from the series. What could this method achieve? (Choose all that apply.) remove a linear trend remove a nonlinear trend remove increasing variance remove seasonal variation 4. Differencing the data one or more times. What could this method achieve? (Choose all that apply.) remove a linear trend remove a nonlinear trend remove increasing variance remove seasonal variation