You are analyzing a time series and want to determine its stationarity. You also want to determine
the order of autoregressive models.
How are the autocorrelation functions used?

A.
ACF as an indication of stationarity,and PACF for the correlation between Xt and Xt-k not
explained by their mutual correlation with X1 through Xk-1.

B.
PACF as an indication of stationarity,and ACF for the correlation between Xt and Xt-k not
explained by their mutual correlation with X1 through Xk-1.

C.
ACF as an indication of stationarity,and PACF to determine the correlation of X1 through Xk-1.

D.
PACF as an indication of stationarity,and ACF to determine the correlation of X1 through Xk-1.