Which of the Following Is/are Disadvantage(s) in Using Counties as Control

Which of the following is/are disadvantage(s) in using counties as control units?

A) they are usually the smallest units for which governmental data are available
B) counties are small enough that sales managers can pinpoint problems
C) the smaller size of counties offers flexibility in shifting counties from one territory to another
D) not all counties are similar in size, sales potential, or ease of market coverage