Four randomly chosen market research companies each produced population estimated 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.

Which one of the following, if true, would best help explain why estimates of the current population of the rapidly growing city varied more than did current population estimates for the two other cities?
(A) Population changes over time are more uniform from one district to another in the rapidly growing city than in the two other cities.
(B) The population of the rapidly growing city is increasing largely as a result of a high birth rate.
(C) The population of the rapidly growing city has a lower average age than the populations of either of the two other cities.
(D) All population estimates of the rapidly growing city were produced first by estimating the current populations of the city’s districts and then by adding those estimates.
(E) Whereas the companies used different methods for estimating the current population of the rapidly growing city, the companies used the same method for the two other cities.

OA IS : A

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i was wondering about E as well

i also answering E but here OA is A

oa is E (source 1000 series)