Observation data {X_1,...,Xn} give the sample partial autocorrelation function values alpha(1)=0.9, alpha(2)=0.5, alpha(3)=D.1, alpha(4)=0.2, alpha(5}=0.1. Based on these values, what is the appropriate order p of the autoregressive process AR[p) to model this dataset? A 2 For process X_n=2X_{n-1}-X_{n=2}+2_n, where Z_n is white noise, which statement is true? A The process is stationary B After difference, the process is stationary C After the second difference, the process is stationary D None of the above