The graph in Figure 3.23 depicts U.S. marriage and divorce rates for selected years. The marriage rates are depicted by the blue bars, and the divorce rates are depicted by the maroon bars. The rates are given as the number of marriages or divorces per 1000 people in the population. 

a. Why do these data consist of marriage and divorce rates rather than total numbers of marriages and divorces? Comment on any trends that you observe in these rates.

b. Redraw the graph as a multiple line chart (one line for marriage rate and one for divorce rate). Briefly discuss the advantages and disadvantages of the two different representations of this particular data set.