Let xi (i from 1 to 10) be ten observations of a random variable X. If Summation of i=1 to 10 (xi-p)

Let xi (i from 1 to 10) be ten observations of a random variable X. If Summation of i=1 to 10 (xi-p)=3 and Summation of i=1 to 10 (xi-p)^2=9, then the Standard deviation of these observations is:
A. 7/10
B. 9/10
C. 4/5
D. √3/5