For the mortality data examined in example 2.2: (a) add another component to the regression in (2.21) that accounts for the particulate count four weeks prior; that is, add pt−4 to the regression in (2.21). state your conclusion. (b) draw a scatterplot matrix of mt, tt, pt and pt−4 and then calculate the pairwise correlations between the series. compare the relationship between mt and pt versus mt and pt−4.