Car dealerships in the state of Fairview have prospered over the term of the current governor: sales are up by 10 percent relative to four years ago. Nevertheless, car manufacturers have found that the proportion of credit they have extended to dealerships that was paid off on time, despite rising over the first two years of this period, has fallen sharply in the latter two years of the governor's term.
Which of the following, if true, most helps to explain the change between the first two and the second two years of the governor's term in the proportion of credit paid off on time?
【选项】
There are essentially constant sources of demand for cars, such as local and state police departments, and sales to these sources have neither increased nor declined especially during the latter two years of the term.
选项是否正确？