Please select ALL correct statement (s) about difference. O a. Taking second differences removes a quartic deterministic trend. O b. `Taking dth difference removes the deterministic trend of a polynomial of degree d. O C. Taking first differences removes a linear deterministic trend. Od. v 2 Y , = V( VY+ ) QUESTION 16 For a time series Y Y2. .... Ym, suppose its sample autocorrelation is 0.95 at lag 1, and 0.6 at lag 10. Which of the following process can best model the above time series? O a. MA(1) O b. AR(1) O C. MA(2) O d. white noise QUESTION 17 For a process Yt = Yt-1 +et - Get -1, where et is a zero-mean white process, let W=Yt-Yt-1. Then Wt is O a. AR(1) O b. white noise O C. MA(1) O d. IMA(1,1 )