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 a triangle is :

Question

( A ) $(-1,\frac{7}{3})$
( B ) $(\frac{1}{3},\frac{7}{3})$
( C ) $(1,\frac{7}{3})$
( D ) $(-\frac{1}{3},\frac{7}{3})$