2. (15 points) Consider the LakeHuron time series from the datasets package in R. This series Xt has annual measurements of the depth of Lake Huron (in feet) from 1875-1972. a. Obtain the autocorrelation (ACF) plot of Lake Huron series for the years 1875-1923, and the ACF of the Lake Huron series for the years 1924-1972. Create a panel plot with these two ACF plots. b. By looking at the panel plot from part a, comment whether the Lake Huron time series from 1875-1972 is stationary