7. For which model are the optimal forecasts given by exponential smoothing ? (A) AR(1) (B) MA(1) (C) ARI(1,1) (D) IMA(1,1) (E) ARMA(1,1) 8. Consider the model Wt=Wt1+at, where Wt=YtYt1. This model is ? (A) ARIMA(1,1,1) (B) ARIMA(1,1,0) (C) ARIMA (1,0,1) (D) ARIMA(0,1,1) (E) ARIMA(1,0,0) 9. (continuation) If this model is written in the form Yt=IYt1+2Yt2+at, then what are the values of 1 and 2 (in terms of )? (A) 1=,2= (B) 1=1+,2=1+ (C) 1=1+,2= (D) 1=,2= (E ) 1=0,2= 10. Recall that Yn(1) denotes the predicted value of Yn+1 at time t=n. If the model is Wt=+at, where Wt=YtYt1, what is Yn(1) ? (A) +yn (B) (C) yn (D) 0 (E) 1