Find the Population Standard Deviation for the Following Data Set $\begin{array} { l l l l l } 21 & 12 & 20 & 15 & 18\end{array}$

Multiple Choice

Find the population standard deviation for the following data set:
$\begin{array} { l l l l l } 21 & 12 & 20 & 15 & 18\end{array}$

A) 3.3
B) 11
C) 13.7
D) 3.7