Suppose $Z_t$ is white noise with mean zero and variance $^2$. Define the stochastic process $X_t$ by the rule $$X_t = X_{t-1} + Z_t$$

Part (a) Find the variance of $X_t$ to two decimal places.

Part (b) Is $X_t$ stationary?

A. No.
B. Yes.
C. It is impossible to tell from the information given.

Part (c) Find the autocovariance of $X_t$ at lag 1, to two decimal places.

Part (d) Which of the following is the autocorrelation function of $X_t$?

????? A B C