$\begin{array}{1 1}(a)\;(x-\large\frac{B}{2})^2\normalsize+(y-\large\frac{B}{2})^2=\normalsize(\large\frac{B}{\sqrt 2})^2\\(b)\;(x-\large\frac{B}{2})\normalsize+(y-\large\frac{B}{2})=\normalsize(\large\frac{B}{\sqrt 3})^2\\(c)\;(x+\large\frac{B}{2})^2\normalsize+(y+\large\frac{B}{2})^2=\normalsize(\large\frac{B}{\sqrt 2})^2\\(d)\;\text{None of these}\end{array}$