$\begin{array}{1 1}(A)\;a = 0 ; b = \large\frac{2}{3} \\(B)\; a = 0 ; b = -\large\frac{2}{3} \\(C)\; a = \large\frac{2}{3} ; b = 0 \\(D)\;a = -\large\frac{2}{3} ; b = 0 \end{array} $