The length of a focal chord of the parabola $y^2=4ax$ making an angle $\theta$ with the axis of the parabola is

Question

$\begin{array}{1 1}(A)\;4a \;cosec ^2 \theta \\(B)\;4a\; \sec^2 \theta \\(C)\;a \;cosec^2 \theta \\(D)\;none\; of\; these \end{array}$