Assume that in a family,each child is equally likely to be a boy or a girl.A family with three children is chosen at random.The probability that the eldest child is a girl given that the family has at least one girl is

Question

$\begin{array}{1 1}(A)\;\frac{1}{2}\quad(B)\;\frac{1}{3}\quad(C)\;\frac{2}{3}\quad(D)\;\frac{4}{7}\end{array}$