Observation data {X_1 .....Xn} give the sample partial autocorrelation function values alpha(1)=0.9, alpha(2)=0.5. alpha(3)=O.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? A2 33 C4 For process X_n=2X_{n-1}-X_{n=2}+Z_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