A data consists of $$n$$ observations: $$x_1, x_2, \ldots, x_n$$. If $$\sum_{i=1}^{n}(x_i + 1)^2 = 9n$$ and $$\sum_{i=1}^{n}(x_i - 1)^2 = 5n$$, then the standard deviation of this data is:

A

5

B

$$\sqrt{7}$$

C

$$\sqrt{5}$$

D

2