If $z_k=\cos\big(\large\frac{k\pi}{10})$$+i\sin(\large\frac{k\pi}{10})$,then $z_1z_2z_3z_4$ equals

Question

$\begin{array}{1 1}(A)\;-1&(B)\;0\\(C)\;1&(D)\;2\end{array} $