The Following Equation $\sqrt{\frac{\sum_{i=1}^{N}\left(x_{i}-u\right)^{2}}{N}}$ , Represents ______

The following equation, $\sqrt{\frac{\sum_{i=1}^{N}\left(x_{i}-u\right) ^{2}}{N}}$ , represents ______.

A) the standard deviation of the sample
B) the standard deviation of the population
C) the standard variance
D) the mean