A researcher computed the mean, the median, and the standard

When a constant number is added to all the elements of a data set, the mean and median increase by the same amount as the added constant, but the standard deviation does not change. Thus, the statistics that change are the mean and median.

If we did not know this fact, we could still find the answer by coming up with an example easy enough to calculate all three quantities. For instance, let’s take a set where all the scores are equal, such as three scores of 10. In the original set, both mean and median are equal to 10; but the standard deviation is 0 (since standard deviation is a measure of how far away the elements are from the mean). When we add 5 to each element, we get three scores of 15; thus, the mean and median both increase to 15, but the standard deviation is still 0.

Answer: D