21.  If a parabola touches the lines y = x and y = -x at A (3,3) and B (1,-1) respectively, then
A)  equation of axis of parabola is 2x + y = 0              B) slope of tangent at vertex is $\frac{1}{2}$
C)  focus is $\left(\frac{6}{5}-\frac{3}{5}\right)$                                                   D)  direct x passes through (1, -2)