Answer:
B. . the data set is a sample
Explanation:
Given that the variance of a data set is correctly computed with the formula using n -1 in the denominator
We know by central limit theorem, that for large samples randomly drawn, the mean of the samples follow a normal distribution.
Here variance of the mean would be variance of population divided by degrees of freedom.
when sample size is n, we have degree of freedom n-1.
Hence only for samples of sizes n, where degree of freedom is n-1 we divide variance by n-1.
Answer is
B. . the data set is a sample