A person has two children. If one of them is boy, then the probability that other is also a boy is

Question

$\begin {array} {1 1} (A)\;\large\frac{1}{2} & \quad (B)\;\large\frac{1}{4} \\ (C)\;\large\frac{1}{3} & \quad (D)\;None\: of \: these \end {array}$