The locus of the point of intersection of tangents of `x^2/a^2 + y^2/b^2 =1` at two points whose eccentric angles differ by `pi/2` is an ellipse whose semi-axes are: (A) `sqrt2 a,sqrt 2 b` (B) `a/sqrt2,b/sqrt2` (C) `a/2,b/2` (D) `2a,2b`