In order to avoid the disadvantages and misleading of the range and the IQR, we need a measure of variability that is based on including all measurements in a data set. The most important and widely used measure of variability in statistics is the standard deviation. To determine the variation of a data set in terms of the amounts, we need to measure the how much each observation deviates from the mean. The variability of a data set is small if the observations are close to their mean, and large if the observations are deviated widely about their mean. The correct answer is C.