A company has offices in two different countries. The 125 employees at location A have a mean commute time of 40 minutes and a standard deviation of 15 minutes. The 250 employees at location B have a mean and standard deviation of 35 and 10 minutes, respectively. Every month, the company takes separate random samples of 20 employees from each location for a survey. Each time, they look at the difference in the mean commute time sampled from each location

Consider the formula: ...
Why is it not appropriate to use this formula for the standard deviation of ...
Choose
A. The samples are not independent of each other.
B. We cannot assume independence for the employees sampled from location A.
C. We cannot assume independence for the employees sampled from location B.