14. The dataset gold (R package TSA, use command data (gold)) contains the daily price of gold (in dollars per troy ounce) for the 252 trading days of the year 2005. (a) Display the time series plot of these data. (b) Let's hypothesize that these data are a realization of a random walk. Plot the first differences of these data. What do you notice? Do the first differences appear stationary? If not, what appears to violate stationarity? (c) (continued from part (a)) Take the natural logarithm of these data, and then take first differences. Now plot the first differences. Do these data appear stationary?