In a Cartesian coordinate system, the vertex of the parabola y=a (x-h) +k is C. The mathematical interest group measures its horizontal span AB and vertical span CD using a horizontal and vertical ruler, with AB=m and CD=n. To determine the opening size of the parabola, the mathematical interest group has two options. Please choose one of the options and complete the process: Option 1: Translate the quadratic function y=a (x-h) +k so that vertex C coincides with the origin O. At this point, the parabolic equation is y=ax At this point, the coordinates of point B 'are ________; Substitute the coordinates of point B 'into y=ax , and solve for a=____; (Represented by an equation containing m and n) Option 2: Let the coordinates of point C be (h, k) At this point, the coordinates of point B are ____; Substitute the coordinates of point B into y=a (x-h) +k, and solve for a=____; (Represented by an equation containing m and n)