If a vertex of a triangle is (1, 1) and the mid-points of two sides through this vertex are (-1, 2) and (3, 2), then the centroid of the triangle is

A

$$\left(-1, \frac{7}{3}\right)$$

B

$$\left(\frac{-1}{3}, \frac{7}{3}\right)$$

C

$$\left(1, \frac{7}{3}\right)$$

D

$$\left(\frac{1}{3}, \frac{7}{3}\right)$$