Four randomly chosen market research companies each produced population estimates for three middle-sized cities; the estimates of each company were then compared with those of the other companies. Two of the cities had relatively stable populations, and for them estimates of current population and of projected population in five years varied little from company to company. However, for the third city, which was growing rapidly, estimates varied greatly from company to company. The passage provides the most support for which one of the following? ['It is more difficult to estimate the population of middle-sized cities than of smaller cities.', 'The market research companies are likely to be equally reliable in estimating the population of stable cities.', "Estimates of a city's future population are likely to be more accurate than are estimates of that city's current population.", 'The rate of change in population of rapidly growing cities does not fluctuate.']