To determine the point at which medians of a triangle intersect one another, it is necessary to determine the equations of the lines for two medians. The coordinates of which two points are used in the calculation of the equation for a given median?

A. the perpendicular bisector of one side and its intersection with a second side

B. the midpoint of one side of a triangle and the midpoint of a second side

C. one vertex of a triangle ahd the point of intersection of the angle bisector and the opposite side

D. one vertex of a triangle and the midpoint of its opposite side