A die is thrown three times.Let X be 'the number of twos seen'.Find the expectation of X.

Question

$\begin{array}{1 1}(A)\;\large\frac{1}{2}\\(B)\;\large\frac{1}{4}\\(C)\;\large\frac{1}{8}\\(D)\;\large\frac{1}{3}\end{array}$